en/subtitles/15. Alerts, Notifications, Application Lifecycle.srt

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[MUSIC]                         

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Stanford University.            
>> Well,                        

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welcome to Stanford CS193P,     
fall of 2017 and                

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18's Lecture number 15. And     
today we have three topics for  

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you, one is Alerts and Action   
Sheets. So that's a way of      

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kind of notifying the user      
when an extraordinary event     

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happens, or to help your user   
make a branching decision       

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where to go now in the app,     
where it's kind of, you know,   

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two or three choices            
of where they can go.           

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The second thing we're gonna    
talk about is Notifications     

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and KVO, that's a way of        
communicating blind and         

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structured inside of our        
MVC and then finally,           

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I'm gonna talk about            
the Application Lifecycle.      

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We already talked about         
the view controller lifecycle,  

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now we're gonna talk about the  
lifetime of your application.   

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All right, so                   
let's start with Alerts and     

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Action Sheets. These two        
things are very similar,        

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the API to use them is almost   
identical, so I always talk     

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about them together. They're    
a little bit different,         

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an alert, it pops up in         
the middle of the screen.       

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They're both modal, they kinda  
take over your screen but,      

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alert pops up in the middle.    

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Generally, whatever the alert   
is telling you or asking you,   

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you're only gonna have one or   
maybe two choices to respond.   

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It would be unusual to have an  
alert, even with three buttons  

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in it. It's usually for         
asynchronous things,            

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things like a network failure   
or something that happens out   

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of the ordinary. You don't      
wanna use an alert as just      

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a way to talk to your user and  
ask them a yes or no question,  

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things like that. Alerts are    
pretty disruptive to the user   

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interface experience because    
they lock out the entire app    

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and force you to deal           
with this thing.                

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So it's not a primary,          

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kind of user                    
interface element,              

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it's more of an emergency       
situation, asynchronous,        

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unusual, that kind of thing.    
Now an action sheet is similar  

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in that it's modal, takes over  
the screen, but here you're     

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almost always gonna have more   
than two choices. This thing    

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slides up from the bottom,      
you're gonna usually have two,  

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three, four, five choices,      
even. And here what you're      

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doing is asking the user to     
make a branching decision.      

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Maybe they've asked             
to take a picture,              

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to get a picture in their app,  
and you wanna know,             

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do you want it                  
from the camera or              

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do you want it from             
the photo library, or           

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do you want it from             
somewhere else?                 

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So they're kind of              
branching right there and       

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you can't really help them      
until they make that decision   

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for you, so that's what an      
action sheet is for. It's not   

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like an alert in that it's for  
unusual circumstances,          

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it's kind of normal branching   
decisions that you would have   

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to make. So here's what         
these things look like,         

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an action sheet slides up       
from the bottom like that,      

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and it can have pretty much     
any number of buttons although  

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obviously, you wouldn't want    
it to fill the whole screen.    

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And then an alert,              
you've seen those,              

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they come up in                 
the middle of the screen,       

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they might even have a little   
text field in them as well.     

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So, again, the API for          
them, i.e, using them,          

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the code you write is almost    
identical, so let's just        

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talk about one of them first    
which is actionSheet. Now,      

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the way both of them work,      
they're just UIViewController.  

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There nothing                   
special about them,             

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they're just                    
UIViewControllers.              

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You know, we learned about how  
to present a UIViewController   

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modally in the last lecture,    
when we put our emoji art       

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controller document             
up modally,                     

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it took over the whole          
screen until we said done.      

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Same thing here                 
with alerts and                 

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action sheets.                  
This UIAlertController is       

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a UIViewController and we're    
just gonna present it using     

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exactly the same method we      
did to present our document.    

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It's called present, but we're  
not gonna create it by getting  

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it out the storyboard like      
what we did with our document.  

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We're gonna create it           
with this initializer,          

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UIAlertController title         
message preferredStyle. And so  

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the title is just the title     
you can see on the left there,  

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the image where                 
the title goes, right?          

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It's the little thing at the    
top Redeploy Cassini, and then  

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the message goes below that     
issue commands to Cassini's     

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guidance system. And then       
the preferredStyle is either    

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actionSheet or alert. So,       
this is what it looks like for  

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actionSheet. Now, you           
create your actionSheet and     

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then you want to add actions,   
these actions correspond to     

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the buttons. So, we have four   
actions right there in our      

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example in what we're gonna     
control Cassini here, and so    

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we're gonna have four times     
we're gonna call a addAction.   

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The argument to addAction,      
there's only one argument,      

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it's a UIAlertAction.           
Which is another object and     

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let's take a look at            
the initializer for             

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UIAlertAction. It takes         
a title, that's gonna be        

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the title that appears on the   
button, a style, we'll talk     

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about the styles in a moment    
here, and then a handler, and   

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a handler is just a closure     
you're gonna give it. It takes  

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the action as an argument so    
that it's in your right hand,   

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and you're gonna do whatever    
you do when that button gets    

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clicked. So,                    
this alert in action,           

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sheets have a very simple API,  
you just put these buttons and  

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the code that goes              
with them on each one.          

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So this handler for, our first  
button there, Orbit Saturn,     

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was just kind of a normal       
button, so its style is         

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UIAlertActionStyle.default.     
And the handler in there,       

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I'm just going to go into       
orbit around Saturn. And        

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that's someone, presumably,     
pressed this button once,       

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and Cassini did that,           
it's finished now,              

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but it did that at one point.   
So this is just the normal      

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default, action here to         
orbit Saturn, right?            

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And I can add another action,   
maybe Explore Titan, now,       

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okay that's not                 
Cassini's mission, but          

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maybe we could allow it if we   
let, make the person logins.    

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So in the handler there, I've   
asked them to log in to verify  

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they really want to divert      
Cassini to Titan, right?        

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How about the next one, which   
is the Closeup of the Sun?      

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Well if I really wanted to      
send, this Cassini off to       

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the Sun, that would almost      
certainly destroy Cassini.      

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And that's why it has a little  
different style there, which    

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is .destructive, you see where  
it says style .destructive? So  

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a .destructive item is gonna    
show up in red text right       

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there and it's any choice       
that is going to make us,       

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kind of significant             
unrecoverable action happen.    

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you're gonna delete             
something out of a database.    

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For example,                    

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That might be a destructive     
action, obviously crashing      

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Cassini into the Sun, that      
would be a destructive action,  

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so that's what .destructive     
style is there. And             

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then, finally, we have this     
cancel action at the bottom,    

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you see it's kinda              
separated a little?             

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And its style is different,     

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.cancel, that's what it causes  
it to be separated. But a very  

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important other thing about     
.cancel is that on the iPad,    

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this thing is not gonna slide   
up from the bottom. It's gonna  

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appear in a popover,            
which we haven't talked about,  

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and we're gonna talk            
all about on Wednesday.         

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But a popover is also modal,    
kinda takes over the screen,    

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but it appears in a little      
window and, in there,           

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you can't have                  
a cancel button,                

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cuz a popover is cancelled      
by touching somewhere else.     

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A popover comes up,             
if you wanna cancel it,         

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you touch somewhere else so     
you don't need a cancel,        

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you don't wanna cancel button.  
That's why it's important to    

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note which of your buttons      
are a cancel button, so         

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that when this                  
appears in a popover,           

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the action sheet here won't     
include that cancel buttons.    

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All right, so                   
we've added our four buttons,   

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now we want this thing to       
slide up to the bottom and      

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let the user choose and         
execute the appropriate         

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handler and we do that          
with that same method,          

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present. It's a ViewController  
method, present,                

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presumably the ViewController   
behind there, you can see that  

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it's got the picture of         
Cassini. That ViewController    

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is presenting this action       
sheet and it's, you know,       

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present the view controller,    
animated true, almost always,   

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and then completion handler     
if you want for which will      

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get called when the animation   
finishes. So that's it,         

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super easy to use an alert.     

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Now let's talk about, this is   
an action sheet, by the way.    

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So let's talk about what it     
looks like on iPad, though,     

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I said it was a popover, this   
is is what it would look like.  

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In this case, you see that      
little redeploy button?         

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And it's kinda small font, but  

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it says redeploy in             
the upper right of the iPad.    

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When I click that, this         
action sheet presented well,    

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first of all how do I get       
it to present like that?        

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And then second of all,         
how do I get it to point to     

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the little redeploy button.     
So I have to do both of those   

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things. The first thing I'm     
going to do is make it present  

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like a popover. And             
to do that, I set the alerts,   

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which is a view control         
remember, I set                 

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it's modalPresentationStyle to  
be .popover. And that's gonna   

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make it to represent as         
a popover. But that's not       

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quite enough because I have to  
make a point at that little     

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redeploy bar button item.       
And the way I do that           

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is I get the alerts popover     
presentation controller,        

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which will be nil if you're     
not presenting it as popover.   

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And one of the vars in          
a popover presentation          

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controller is the barButton     
item that is presenting it.     

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You can also specify            
a rectangle,                    

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an arbitrary rectangle and      

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the little triangle will point  
at that when it appears.        

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You can also specify which      
direction the little arrow is   

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allowed to point, left, right,  
up or down. And in that way     

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you can control the way         
that this popover presents.     

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Does this make sense?           
Now you're probably saying,     

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well I need to put if I'm on    
iPad then do this around this,  

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right? Because obviously        
on an iPhone I don't want       

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this thing to be a popover.     
But actually, you don't have    

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to do that, because this exact  
same code will still slide up   

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from the bottom on an iPhone.   
Now, why does that happen?      

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We've specifically asked for    
the popover presentation style  

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there and we specified the      
barButton item and all that.    

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Well, iOS automatically does    
what we called adapting         

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to the environment its in.      
Both the trait environment,     

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right, compact width and        
or not, and                     

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all that stuff we talked about  
before, but also the platform   

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its on to some extent.          
And so here it notices,         

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well I'm on an iPhone,          
I don't do popovers. Actually,  

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you can do popovers on iPhone   
as we'll talk about, but        

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you have to do extraordinary    
things to do that. So           

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in the normal case of events    
it doesn't do popover,          

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so it comes over in             
it's normal way. So             

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if you're doing a popover, and  

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you have a universal app that   
runs on both iPad and iPhone,   

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you're gonna put this modal     
presentation stuff in there.    

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All right, so                   
let's talk about alert.         

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Same exact constructor,         
you just say preferred style    

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alert, same exact               
adding actions. And             

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here I am adding                
my cancel button,               

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I'm marking it as .cancel plus  
importing in alert because it   

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doesn't hide the cancel button  
in any case cuz alerts look     

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exactly the same on both iPads  
and iPhones. And then I'm       

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gonna add another action here   
which is my login button.       

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Now, my login button is going   
to use that text field,         

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you see that text field? So     
how the heck did I get a text   

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field to appear in              
the middle of my alert?         

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Well, I just said               
alert.addTextField, and         

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00:10:34,134 --> 00:10:37,268
the argument to that add        
text field is a closure         

217
00:10:37,337 --> 00:10:38,937
that passes the text            
field to you and                

218
00:10:39,005 --> 00:10:42,440
allows you to configure it.     
This is a password for          

219
00:10:42,509 --> 00:10:44,809
redeploying Cassini off         
to the Sun, or titan, or        

220
00:10:44,878 --> 00:10:48,713
something. So I want it to      
have secure text entry, so      

221
00:10:48,781 --> 00:10:51,649
I'm using the text field var,   
there is secure text entry      

222
00:10:51,718 --> 00:10:54,718
which is part of the text       
input traits protocol that      

223
00:10:54,787 --> 00:10:58,188
text field implements. And you  
could do this more than once,   

224
00:10:58,257 --> 00:10:59,690
you can have more               
than one text field.            

225
00:10:59,759 --> 00:11:03,594
I recommend against that, and   
I generally recommend against   

226
00:11:03,663 --> 00:11:06,664
using an alert as a login       
screen. Don't do that for       

227
00:11:06,733 --> 00:11:07,398
your final project.             

228
00:11:07,467 --> 00:11:08,399
If you have a login screen,     

229
00:11:08,468 --> 00:11:12,169
make it a normal part of your   
UI, don't have it be an alert.  

230
00:11:12,238 --> 00:11:15,973
But anyway, once you get this   
text field added with this and  

231
00:11:16,042 --> 00:11:19,143
configured, then how do you     
get the text out when someone   

232
00:11:19,212 --> 00:11:22,213
types the text. Well in your    
handler of the action for       

233
00:11:22,281 --> 00:11:26,550
login right there, I'm just     
gonna use the var that's in     

234
00:11:26,619 --> 00:11:29,653
alert called text field,        
it's an array of all the text   

235
00:11:29,722 --> 00:11:32,189
fields. I only have one so I'm  
going to get the first one and  

236
00:11:32,258 --> 00:11:33,725
then I'm going to get           
the text out of it.             

237
00:11:35,361 --> 00:11:36,161
Couldn't be simpler.            

238
00:11:37,764 --> 00:11:41,766
All right, I almost hesitate    
to show you the alert with      

239
00:11:41,834 --> 00:11:43,968
the text field in there         
because it makes you say,       

240
00:11:44,036 --> 00:11:45,970
that's a great way to get       
text from the user, but         

241
00:11:46,039 --> 00:11:50,107
again alerts are disruptive so  
don't use them for that.        

242
00:11:50,176 --> 00:11:53,111
All right, and I'm gonna        
present this in exact the same  

243
00:11:53,179 --> 00:11:56,948
way I presented the action      
sheet with the present method,  

244
00:11:57,017 --> 00:11:59,817
which presents. Just all        
present does is it presents     

245
00:11:59,885 --> 00:12:03,021
a view controller modaly?       
And of course this is a modal   

246
00:12:03,089 --> 00:12:05,790
because the whole screen        
is dimmed out, except for       

247
00:12:05,859 --> 00:12:10,061
this middle box.                
All right, and as I said,       

248
00:12:10,130 --> 00:12:13,431
on the iPad,                    
alerts look exactly the same.   

249
00:12:13,500 --> 00:12:18,402
There's no difference.          
So that's alerts, so let's put  

250
00:12:18,471 --> 00:12:21,305
an alert in EmojiArt, just so   
we could see this in action.    

251
00:12:21,374 --> 00:12:25,844
And here's the alert I'm gonna  
put in. Right now, EmojiArt,    

252
00:12:25,912 --> 00:12:29,214
if you drag any image in        
to EmojiArt, it will work.      

253
00:12:29,282 --> 00:12:31,148
And that's because I            
have that image fetcher,        

254
00:12:31,217 --> 00:12:31,950
remember that and               

255
00:12:32,018 --> 00:12:35,086
the image fetcher allows you    
to specify a back-up image.     

256
00:12:35,154 --> 00:12:38,556
And so if I can't get           
the image from the URL          

257
00:12:38,625 --> 00:12:39,924
with the image fetcher,         
no problem,                     

258
00:12:39,993 --> 00:12:42,326
I'll use the back-up image and  
create a one on disk and        

259
00:12:42,395 --> 00:12:43,795
use that as the URL.            

260
00:12:43,863 --> 00:12:47,765
Well that solution doesn't      
work too well in iCloud drive.  

261
00:12:47,834 --> 00:12:50,969
Because I create an EmojiArt    
document on my iPad,            

262
00:12:51,037 --> 00:12:53,304
I drag in something that I      
couldn't get it's URL so        

263
00:12:53,372 --> 00:12:56,206
I just put the image locally.   
I put it on iCloud Drive,       

264
00:12:56,275 --> 00:12:59,243
I go over to my iPhone,         
I look at it, I can't see it.   

265
00:12:59,312 --> 00:13:02,413
Because it's using the backup   
image which is on my iPad. So   

266
00:13:02,482 --> 00:13:05,983
I'm gonna fix my EmojiArt       
just to simply not accept       

267
00:13:06,052 --> 00:13:09,086
those things. So if you drag    
in something that I can't get   

268
00:13:09,155 --> 00:13:10,555
its image from the URL,         

269
00:13:10,623 --> 00:13:13,257
I'm just gonna reject it.       
Now I could just quietly        

270
00:13:13,326 --> 00:13:16,594
reject it. And the user would   
probably be like, what's going  

271
00:13:16,663 --> 00:13:18,829
on? I keep dragging this and    
it won't take it.               

272
00:13:18,898 --> 00:13:20,431
But it'd be much better         
if I put up an alert and        

273
00:13:20,500 --> 00:13:23,668
said, I couldn't get the image  
from that URL, sorry, okay so   

274
00:13:23,736 --> 00:13:26,771
that's what we're gonna do.     
However, once I got used to     

275
00:13:26,840 --> 00:13:30,541
that, then I probably don't     
want it coming up every time.   

276
00:13:30,610 --> 00:13:33,611
Because I do get the feedback   
when I drag in a bad image,     

277
00:13:33,679 --> 00:13:35,079
it just does nothing.           

278
00:13:35,148 --> 00:13:37,381
And eventually I'll learn,      
that one I can't drag in,       

279
00:13:37,450 --> 00:13:39,250
I'll have to pick               
something else. And so          

280
00:13:39,318 --> 00:13:41,151
I'm going to have my            
alert have two buttons.         

281
00:13:41,220 --> 00:13:44,822
One is keep warning me about    
this, and the other one is      

282
00:13:44,890 --> 00:13:47,491
stop warning me about this.     
Those are the only two          

283
00:13:47,560 --> 00:13:50,227
buttons on my alert. The alert  
is otherwise just going to say  

284
00:13:50,296 --> 00:13:51,763
I couldn't get the image        
from that URL.                  

285
00:13:51,831 --> 00:13:54,699
So that's what we're going to   
build so let's go do that.      

286
00:13:58,170 --> 00:14:00,738
To our emojiArt, here we are.   
So here's emojiArt,             

287
00:14:00,806 --> 00:14:03,441
if you remember, we do all of   
our image dropping down at      

288
00:14:03,509 --> 00:14:07,244
the bottom here in our draft    
interaction delegates here.     

289
00:14:07,313 --> 00:14:08,479
Right here is                   
the imageFetcher,               

290
00:14:08,548 --> 00:14:12,383
here's what we dropped when we  
get the URL, we fetch it with   

291
00:14:12,452 --> 00:14:15,586
the imageFetcher. But if we     
get an image, we use it as      

292
00:14:15,654 --> 00:14:18,755
a backup image. So we're        
not gonna do this anymore,      

293
00:14:18,824 --> 00:14:22,393
I'm gonna in fact, stop using   
the imageFetcher all together.  

294
00:14:22,461 --> 00:14:25,329
So I'm just gonna comment that  
imageFetcher out. Instead       

295
00:14:25,398 --> 00:14:28,132
what I'm gonna do is what you   
did probably in your homework,  

296
00:14:28,201 --> 00:14:31,135
hopefully. And                  
what we did last week in, or    

297
00:14:31,203 --> 00:14:33,170
the week before,                
in the ImageViewController,     

298
00:14:33,239 --> 00:14:35,740
which I'm just gonna fetch      
this thing directly.            

299
00:14:35,808 --> 00:14:37,608
Now one thing I have to be      
careful about here is I don't   

300
00:14:37,677 --> 00:14:42,312
wanna block the main queue.     
And this closure, the one that  

301
00:14:42,381 --> 00:14:46,751
load objects, plural, that      
I do on a session. This one     

302
00:14:46,820 --> 00:14:50,687
is a convenience method,        
it calls on the main queue.     

303
00:14:50,756 --> 00:14:53,357
So this closure is on the main  
queue doing this. So I do not   

304
00:14:53,426 --> 00:14:56,894
want that, I want to dispatch   
off of the main queue. So I'm   

305
00:14:56,962 --> 00:15:01,765
gonna do DispatchQueue.global   
queue. I'm gonna get            

306
00:15:01,834 --> 00:15:05,803
do userInitiated, because the   
user did just drop this and     

307
00:15:05,872 --> 00:15:08,439
is presumably asking me         
to go do it right now.          

308
00:15:08,507 --> 00:15:11,142
And I'm going to                
asynchronously perform this     

309
00:15:11,210 --> 00:15:15,846
block. And what I'm gonna do    
in this block is go try and     

310
00:15:15,915 --> 00:15:18,949
fetch that image. So I'm gonna  
say, if I can let the image     

311
00:15:19,018 --> 00:15:24,688
data equal trying to ask        
the data to get the contents    

312
00:15:24,757 --> 00:15:28,559
of this URL, but I'm actually   
gonna use the image URL.        

313
00:15:28,628 --> 00:15:32,263
As you learn in your homework,  
sometimes you gotta massage     

314
00:15:32,332 --> 00:15:35,733
that URL a little bit to get    
the right thing out of there.   

315
00:15:35,802 --> 00:15:39,737
And then I'm going to let       
image = UIImage from that       

316
00:15:39,805 --> 00:15:43,841
data, if I can, imageData.      
And if I was successfully able  

317
00:15:43,910 --> 00:15:44,676
to do all of that,              

318
00:15:44,744 --> 00:15:46,410
and I'm doing this all          
in another thread, so           

319
00:15:46,478 --> 00:15:50,915
it's nice I'm not blocking      
the UI. Now I can use this URL  

320
00:15:50,984 --> 00:15:52,483
absolutely normally.            
Of course,                      

321
00:15:52,552 --> 00:15:56,888
I wanna now dispatch back to    
the main queue. All right?      

322
00:15:56,956 --> 00:16:01,059
Cuz I'm gonna do UI thing,      
which is I'm gonna say,         

323
00:16:01,127 --> 00:16:06,096
self.emojiArtBackgroundImage =  
[url, image].                   

324
00:16:06,165 --> 00:16:11,069
I'm also gonna do               
docself.documentChanged.        

325
00:16:13,472 --> 00:16:17,107
This is calling the method      
that used to be called save.    

326
00:16:17,176 --> 00:16:19,676
And then after the last         
lecture I told you I was going  

327
00:16:19,745 --> 00:16:22,446
to use delegation to            
automatically track changes.    

328
00:16:22,515 --> 00:16:23,381
Well this is one                
of the changes I                

329
00:16:23,449 --> 00:16:25,182
have to track. If you change    
the background image,           

330
00:16:25,251 --> 00:16:27,050
I have to let the document      
know that it has changed.       

331
00:16:27,119 --> 00:16:29,520
And we're going to look at      
document change in a little     

332
00:16:29,589 --> 00:16:32,256
bit later demo, today.          
It's exactly the same as save,  

333
00:16:32,325 --> 00:16:34,157
I just renamed it               
document change. But            

334
00:16:34,226 --> 00:16:37,128
we definitely want to do that   
in here. Now, here's the rub.   

335
00:16:37,197 --> 00:16:40,797
Here's the alert magic.         
If I couldn't do that,          

336
00:16:40,866 --> 00:16:43,800
if I was unable to get that     
image out of there. Now I       

337
00:16:43,869 --> 00:16:47,638
wanna put up an alert instead   
of using that backup image. So  

338
00:16:47,707 --> 00:16:52,610
I'm going to say here,          
self.presentBadURLWarning,      

339
00:16:52,679 --> 00:16:56,647
and I'm going to actually       
pass the url along.             

340
00:16:56,716 --> 00:16:58,482
Now why am I passing            
that url along?                 

341
00:16:58,550 --> 00:17:01,518
I'm not gonna do this for time  
reasons, but you know what      

342
00:17:01,587 --> 00:17:04,689
would be a really cool thing    
is someone drags something in,  

343
00:17:04,757 --> 00:17:07,258
it puts up the alert. They're   
like, don't warn me again.      

344
00:17:07,326 --> 00:17:10,661
And they say stop. But then     
they drag another one in and    

345
00:17:10,729 --> 00:17:13,864
it doesn't work. Then they      
try a different one and         

346
00:17:13,933 --> 00:17:18,035
it doesn't work. And they're    
like, it's broken. They've      

347
00:17:18,104 --> 00:17:20,838
kind of forgotten that they     
said stop warning me that.      

348
00:17:20,906 --> 00:17:22,940
So somehow you might            
want that alert to come         

349
00:17:23,009 --> 00:17:26,644
back on. At some point, right?  
And what would be a cool way    

350
00:17:26,713 --> 00:17:31,082
to do that? How about if they   
drag the same url in twice.     

351
00:17:31,150 --> 00:17:34,351
Because that's them saying,     
drag it in. It didn't work.     

352
00:17:34,420 --> 00:17:37,355
Why didn't it work? Let me try  
again. Well if they're trying   

353
00:17:37,423 --> 00:17:39,657
again they probably             
forgot about that alert.        

354
00:17:39,725 --> 00:17:41,692
Maybe, maybe not,               
but it's likely.                

355
00:17:41,761 --> 00:17:44,428
So that's the kinda thing       
you can do in your UI that's    

356
00:17:44,497 --> 00:17:47,130
a little tricky, that allows    
them to turn things like that   

357
00:17:47,199 --> 00:17:49,633
back on without having to go    
to settings somewhere and       

358
00:17:49,702 --> 00:17:51,568
turn it on,                     
which is really cumbersome.     

359
00:17:51,637 --> 00:17:55,005
It's just kind of using their   
natural things that they're     

360
00:17:55,074 --> 00:17:58,208
doing. In the UI, you can       
make decisions like this.       

361
00:17:58,277 --> 00:17:59,243
So I just kinda want to give    
you just kind of a classic      

362
00:17:59,244 --> 00:18:00,210
Does that make sense?           

363
00:18:00,279 --> 00:18:02,880
example of that. So that's      
why I might pass this URL on,   

364
00:18:02,949 --> 00:18:05,716
because I might want to check   
to see if it's the same URL.    

365
00:18:05,785 --> 00:18:08,419
Now I'm not gonna do that       
today, for time constraints.    

366
00:18:08,488 --> 00:18:11,189
But I just wanted to give you   
the idea you could do that.     

367
00:18:11,257 --> 00:18:14,124
All right, so let's do          
our private func here,          

368
00:18:14,193 --> 00:18:16,360
presentBadURLWarning for URL.   

369
00:18:18,631 --> 00:18:19,864
And what am I                   
gonna do in here?               

370
00:18:19,932 --> 00:18:22,232
I'm gonna create that           
alert and present it.           

371
00:18:22,301 --> 00:18:24,335
That's why we're here,          
is to learn about alerts.       

372
00:18:24,403 --> 00:18:27,504
So creating alert is just       
creating that view controller.  

373
00:18:27,573 --> 00:18:31,909
So let alert =                  
UIAlertController.              

374
00:18:31,978 --> 00:18:34,778
Why they didn't call it         
UIAlertViewController,          

375
00:18:34,847 --> 00:18:38,616
I do not know. They did not.    
So UIAlertController, and       

376
00:18:38,685 --> 00:18:41,252
the constructor for it here,    
we always want this one         

377
00:18:41,320 --> 00:18:44,054
down here. You can see this     
one's that NS coder stuff we    

378
00:18:44,123 --> 00:18:47,290
learned about before. This is   
is kind of an old style thing.  

379
00:18:47,359 --> 00:18:51,161
We always want this one right   
here, that gives us the title,  

380
00:18:51,230 --> 00:18:53,697
the message that's              
gonna go in there.              

381
00:18:53,766 --> 00:18:57,468
And the style, whether it's an  
action sheet or an alert. And   

382
00:18:57,537 --> 00:18:59,536
so our title here,              
what's happening?               

383
00:18:59,605 --> 00:19:02,005
Well, they dropped an image.    
We couldn't get the data.       

384
00:19:02,074 --> 00:19:06,944
So I'm gonna call this thing    
Image Transfer Failed, maybe.   

385
00:19:07,013 --> 00:19:12,416
It's actually very important    
to pick good phraseology here,  

386
00:19:12,484 --> 00:19:14,619
cuz you don't wanna freak       
your user out. My gosh,         

387
00:19:14,687 --> 00:19:16,387
what did I do or whatever?      
You wanna try and               

388
00:19:16,455 --> 00:19:18,889
give them something that        
gives them the authority,       

389
00:19:18,958 --> 00:19:21,692
kind of project some authority  
that this, don't worry,         

390
00:19:21,760 --> 00:19:24,662
this happened. I understand     
it and here's your options.     

391
00:19:24,730 --> 00:19:26,497
But not something that's so     
technical that they're like,    

392
00:19:26,566 --> 00:19:30,067
what? Like if we say something  
like couldn't load from URL.    

393
00:19:30,136 --> 00:19:32,803
Okay well users don't even      
know what URLs are. So          

394
00:19:32,871 --> 00:19:34,338
you wouldn't wanna              
put URL in here.                

395
00:19:34,407 --> 00:19:35,906
You see what I'm saying? So     

396
00:19:35,974 --> 00:19:38,675
image transfer, when they're    
dragging presumably they're     

397
00:19:38,744 --> 00:19:42,079
trying to transfer that image.  
You know, it's a good name.     

398
00:19:42,148 --> 00:19:45,749
Maybe we might even wanna say,  
image drop failed, possibly.    

399
00:19:45,818 --> 00:19:47,818
You know, this is the kind      
of thing you user test and      

400
00:19:47,886 --> 00:19:49,653
you try and get the right       
words. Of course,               

401
00:19:49,722 --> 00:19:51,889
the other thing here is         
we wanna localize this.         

402
00:19:51,958 --> 00:19:54,792
And I'm gonna talk, hopefully   
the week after Thanksgiving,    

403
00:19:54,861 --> 00:19:57,461
about how to localize your app  
for other languages. Because    

404
00:19:57,530 --> 00:20:00,163
we want our app to run in as    
many languages as possible, so  

405
00:20:00,232 --> 00:20:02,866
we have to make that string     
be able to be localizable.      

406
00:20:02,935 --> 00:20:05,903
And it's quite easy to do in    
iOS, but we'll learn about      

407
00:20:05,971 --> 00:20:08,639
that in a couple weeks. And     
now here's the message where    

408
00:20:08,707 --> 00:20:10,540
I'm gonna tell them more        
about what happened.            

409
00:20:10,609 --> 00:20:15,078
So here I'm kind of saying      
what happened here, which is    

410
00:20:15,147 --> 00:20:20,350
that I couldn't transfer the    
dropped image from its source.  

411
00:20:20,419 --> 00:20:22,086
Again, I'm not mentioning       
the term URL or                 

412
00:20:22,154 --> 00:20:25,356
anything like that.             
I'm just doing that. And        

413
00:20:25,425 --> 00:20:27,824
of course this is an alert,     
not an action sheet, so         

414
00:20:27,893 --> 00:20:30,995
we'll say that. So this         
creates this view controller,   

415
00:20:31,063 --> 00:20:35,499
and then I'm just going to      
present I am a view controller  

416
00:20:35,568 --> 00:20:39,870
here, present. So I can         
call this method on myself,     

417
00:20:39,939 --> 00:20:41,839
it's a view controller method,  
present.                        

418
00:20:41,908 --> 00:20:45,075
I'm gonna present the alert,    
animated true, and              

419
00:20:45,144 --> 00:20:48,678
I don't have any completion     
thing I wanna do so I'll just   

420
00:20:48,747 --> 00:20:52,783
leave that off. But of course   
I need to add my buttons here.  

421
00:20:52,851 --> 00:20:53,784
So what buttons                 
are we gonna have?              

422
00:20:53,853 --> 00:20:57,020
Well, remember I'm gonna have   
keep warning me and stop        

423
00:20:57,089 --> 00:21:00,257
warning me. Okay so, let's do   
the keep warning one first.     

424
00:21:00,326 --> 00:21:03,226
So I'm just gonna say           
alert.addAction and             

425
00:21:03,295 --> 00:21:06,897
remember the action you can     
see takes us one argument,      

426
00:21:06,966 --> 00:21:10,635
which is a UIAlertAction. And   
that has only one initializer,  

427
00:21:10,703 --> 00:21:13,370
which is these one right here.  
So make it so                   

428
00:21:13,439 --> 00:21:18,509
you can see even better here.   
All right,                      

429
00:21:18,578 --> 00:21:21,778
so it wants the title. That's   
the title of the button. So     

430
00:21:21,847 --> 00:21:25,649
this is the one where I'm       
going to keep warning           

431
00:21:25,718 --> 00:21:29,720
the person. And the style for   
this is just default,           

432
00:21:29,789 --> 00:21:32,890
this is the normal default      
button. Keep Warning isn't      

433
00:21:32,958 --> 00:21:34,891
anything special, it's not      
gonna change anything, really.  

434
00:21:34,960 --> 00:21:36,193
We just keep on warning them.   

435
00:21:36,262 --> 00:21:37,961
And I actually don't            
need a handler here,            

436
00:21:38,030 --> 00:21:39,296
cuz I'm not gonna do anything,  

437
00:21:39,364 --> 00:21:40,764
if you keep saying              
Keep Warning me,                

438
00:21:40,833 --> 00:21:42,132
cuz that's what                 
I do by default.                

439
00:21:42,201 --> 00:21:47,438
So I'm just gonna get rid of    
that, and that's my action. So  

440
00:21:47,507 --> 00:21:50,941
a lot of time cancel            
buttons and okay buttons,       

441
00:21:51,009 --> 00:21:53,010
they don't have any action,     
they don't do anything. And     

442
00:21:53,078 --> 00:21:55,645
that's, this is kind of like    
an okay button in a way. But    

443
00:21:55,714 --> 00:22:01,519
our other button alert add      
action, UIAlertAction.          

444
00:22:01,587 --> 00:22:03,888
This one does have a handler,   
and                             

445
00:22:03,956 --> 00:22:07,958
let's talk about how we're      
going to implement this.        

446
00:22:11,063 --> 00:22:14,231
Let's see, now it's on one      
page there. So here this, this  

447
00:22:14,300 --> 00:22:17,968
string is Stop Warning. Now if  
I just have Stop Warning and    

448
00:22:18,037 --> 00:22:21,038
Keep Warning, that's really     
not enough information for      

449
00:22:21,106 --> 00:22:22,272
people to understand.           

450
00:22:22,341 --> 00:22:25,409
What do you mean Stop Warning?  
You know what I mean? So        

451
00:22:25,478 --> 00:22:28,079
I actually wanna add a little   
more to my message up here.     

452
00:22:28,147 --> 00:22:32,916
I'm gonna say something         
along the lines of,             

453
00:22:32,985 --> 00:22:36,487
show this warning               
in the future?                  

454
00:22:36,555 --> 00:22:40,024
Now, Keep Warning and Stop      
Warning make a lot more sense.  

455
00:22:41,227 --> 00:22:44,528
However, you don't              
want this to be yes and         

456
00:22:44,596 --> 00:22:47,698
no. Having buttons in           
an alert, yes and no.           

457
00:22:47,767 --> 00:22:50,567
That forces the person          
to go carefully read and        

458
00:22:50,636 --> 00:22:53,971
parse the message you said.     
And they don't get any double   

459
00:22:54,040 --> 00:22:56,473
check that they read it right   
before they press yes or no.    

460
00:22:56,542 --> 00:23:00,176
So always try to pick things    
that are more descriptive than  

461
00:23:00,245 --> 00:23:03,747
yes or no, like keep this       
warning, stop this warning.     

462
00:23:03,816 --> 00:23:05,215
Okay you still                  
have to be brief,               

463
00:23:05,284 --> 00:23:07,751
you don't want these buttons    
to have ten words on them.      

464
00:23:07,820 --> 00:23:09,553
So it's a compromise            
between brevity and             

465
00:23:09,621 --> 00:23:11,054
making sure the person          
understands.                    

466
00:23:11,123 --> 00:23:14,391
Now I'm gonna call this         
destructive because it's going  

467
00:23:14,459 --> 00:23:17,294
to stop it doing something      
that it does pretty much        

468
00:23:17,363 --> 00:23:19,963
permanently unless I go         
add that feature where          

469
00:23:20,032 --> 00:23:23,400
I compare the URLs and turn it  
back on. So I'm gonna set this  

470
00:23:23,469 --> 00:23:25,970
to destructive. So it's gonna   
turn out red. It's gonna        

471
00:23:26,038 --> 00:23:28,339
make the user think a little    
bit before they press that,     

472
00:23:28,407 --> 00:23:31,609
which is exactly what I want.   
And how about our handler       

473
00:23:31,677 --> 00:23:35,446
here. So the handler passes     
this action back to us. And     

474
00:23:35,514 --> 00:23:38,448
we usually don't                
need that because               

475
00:23:38,517 --> 00:23:42,018
we can just capture it in       
using closure capture,          

476
00:23:42,087 --> 00:23:47,224
we capture this little action.  
Although, you know, since you   

477
00:23:47,293 --> 00:23:49,893
usually add it like this, you   
don't actually have a local     

478
00:23:49,962 --> 00:23:52,328
var to this action. So it's     
kinda nice that it passes it.   

479
00:23:52,397 --> 00:23:55,166
We don't need it in any case.   
All we need to do here is set   

480
00:23:55,234 --> 00:23:57,801
some var that says,             
suppress these warnings.        

481
00:23:57,870 --> 00:24:03,173
So I'm gonna say self.          
suppressBadURLWarnings = true,  

482
00:24:03,242 --> 00:24:08,011
so I need a var for this.       
So I'll put that up here,       

483
00:24:08,080 --> 00:24:12,149
private var, I think I copy     
and pasted it, yeah I did.      

484
00:24:12,217 --> 00:24:14,118
Equals, of course it's          
gonna start out false,          

485
00:24:14,187 --> 00:24:15,385
we're not gonna suppress it.    

486
00:24:15,454 --> 00:24:22,226
And all I'm gonna do is, not    
do this method if that's true,  

487
00:24:22,294 --> 00:24:27,564
so I'm gonna say if             
suppressBadURLWarnings,         

488
00:24:27,633 --> 00:24:33,103
not then do this. So            

489
00:24:33,172 --> 00:24:36,239
that's it, that's the entire    
implementation of this,         

490
00:24:36,308 --> 00:24:42,946
let's go see this working.      
Here's our app right here,      

491
00:24:43,014 --> 00:24:46,717
let's open up our Apple Bees    
document right here. Here it    

492
00:24:46,785 --> 00:24:50,887
is, and let's try dragging      
in an image, that works.        

493
00:24:50,956 --> 00:24:53,423
How about I think this one      
works, this one has an URL.     

494
00:24:53,492 --> 00:24:56,860
So we drag it in, it loads      
it up, excellent, it worked,    

495
00:24:56,929 --> 00:24:59,863
it's got a high resolution      
image, that's good.             

496
00:24:59,932 --> 00:25:01,865
How about let's drag in         
one that doesn't work,          

497
00:25:01,934 --> 00:25:05,168
how about this one? This one    
happens to not have a good      

498
00:25:05,237 --> 00:25:08,071
URL, all right,                 
we got an alert here.           

499
00:25:08,140 --> 00:25:11,074
Couldn't transfer the dropped   
image from the source,          

500
00:25:11,143 --> 00:25:14,044
show this warning in the        
future, keep the warning, or    

501
00:25:14,112 --> 00:25:17,581
stop warning, so I will         
keep warning. That's good,      

502
00:25:17,650 --> 00:25:21,251
let's try another one,          
how about this one down here?   

503
00:25:21,320 --> 00:25:24,355
That's also no good, now I'm    
tired of this warning, so       

504
00:25:24,423 --> 00:25:28,458
I'm gonna say, stop warning     
me. Now let's try and           

505
00:25:28,527 --> 00:25:32,162
drag this bad one in            
again right here,               

506
00:25:32,231 --> 00:25:36,333
no warning. All right,          
so that's that,                 

507
00:25:36,401 --> 00:25:38,869
let's get back to our slides,   
and                             

508
00:25:38,938 --> 00:25:42,072
action sheet is exactly         
the same, right?                

509
00:25:42,140 --> 00:25:45,843
You're gonna do exactly         
the same thing over there.      

510
00:25:45,911 --> 00:25:51,515
All right, our next topic here  
is notifications and KVO.       

511
00:25:51,583 --> 00:25:55,152
So if you remember back to      
the MVC talk I did at the very  

512
00:25:55,220 --> 00:25:58,055
beginning, like, second         
lecture. I had this little      

513
00:25:58,124 --> 00:26:00,657
radio station, the little       
orange things right there.      

514
00:26:00,726 --> 00:26:04,862
I said, well, the model can't   
talk to its controller, so it   

515
00:26:04,930 --> 00:26:07,531
has to use other mechanisms.    
And why can't the model talk    

516
00:26:07,600 --> 00:26:11,402
to the controller? Because the  
model is UI independent and     

517
00:26:11,470 --> 00:26:13,570
the component is                
fundamentally UI dependent.     

518
00:26:13,639 --> 00:26:16,005
So there's no way for them      
to talk in that direction.      

519
00:26:16,074 --> 00:26:18,541
The controller can talk to the  
model, but not the other way,   

520
00:26:18,610 --> 00:26:21,378
so we have this blind and       
structured way of doing it.     

521
00:26:21,447 --> 00:26:24,248
By the way, a view might        
also want to use this           

522
00:26:24,316 --> 00:26:26,850
radio station to talk to its    
controller because the view     

523
00:26:26,919 --> 00:26:28,618
can't also talk to              
its controller for              

524
00:26:28,687 --> 00:26:32,322
a different reason. The view    
is generic, and the controller  

525
00:26:32,391 --> 00:26:35,725
is specific UI. So there's      
no way generic items like       

526
00:26:35,794 --> 00:26:38,661
buttons could know anything     
about a particular controller.  

527
00:26:38,730 --> 00:26:41,631
So for both reasons, the        
viewing model ca't talk to      

528
00:26:41,700 --> 00:26:44,334
the controller, controller      
talking to them is okay, but    

529
00:26:44,403 --> 00:26:45,369
ca't do the other way. So       

530
00:26:45,437 --> 00:26:48,005
they both could use this radio  
station model. And there's      

531
00:26:48,073 --> 00:26:50,974
really two ways to do radio     
stations, notifications and     

532
00:26:51,043 --> 00:26:54,144
KVO, KVO stands for             
key value observing.            

533
00:26:54,212 --> 00:26:57,213
So we're gonna talk about this  
radio station, by the way,      

534
00:26:57,282 --> 00:26:59,983
only I call it radio station,   
it's not called radio station   

535
00:27:00,052 --> 00:27:02,586
in the doc. But a radio         
station is a good analogy for   

536
00:27:02,654 --> 00:27:05,789
the kind of communication       
that's going on between these   

537
00:27:05,858 --> 00:27:10,661
things. All right, here's       
notifications, the first of     

538
00:27:10,729 --> 00:27:13,931
these. So a notification        
is essentially just             

539
00:27:13,999 --> 00:27:17,667
a way you're gonna register     
a closure to get called when    

540
00:27:17,736 --> 00:27:22,072
someone broadcasts on a named   
radio station. That's all it    

541
00:27:22,140 --> 00:27:25,509
is, very simple, you can see    
how it's immediately blind.     

542
00:27:25,578 --> 00:27:27,377
Nobody knows who's              
any classes,                    

543
00:27:27,446 --> 00:27:31,681
all we're talking about here    
is this radio station. And      

544
00:27:31,750 --> 00:27:32,449
it's very flexible,             

545
00:27:32,518 --> 00:27:35,318
cuz you just plop a closure     
down there, and it just calls   

546
00:27:35,387 --> 00:27:37,854
it when someone broadcasts      
on that radio station. And      

547
00:27:37,923 --> 00:27:41,659
it's also possible to           
broadcast music on a radio      

548
00:27:41,727 --> 00:27:44,461
station. In other words,        
when you broadcast,             

549
00:27:44,529 --> 00:27:47,630
you can put information across  
the radio station as well,      

550
00:27:47,699 --> 00:27:48,798
which is kinda cool.            

551
00:27:48,867 --> 00:27:51,901
All right, so this is what      
the function to say I wanna     

552
00:27:51,970 --> 00:27:54,471
listen to a radio               
station looks like, this        

553
00:27:54,540 --> 00:27:59,543
code you see up right here.     
All of this stuff is done via   

554
00:27:59,611 --> 00:28:03,447
this thing right here,          
NotificationCenter.default.     

555
00:28:03,516 --> 00:28:05,181
You see that                    
NotificationCenter.default,     

556
00:28:05,250 --> 00:28:08,285
and I'm using it down here. So  
NotificationCenter is a thing   

557
00:28:08,354 --> 00:28:10,988
that you use to both sign up    
to listen to a radio station,   

558
00:28:11,057 --> 00:28:13,456
and to broadcast on             
a radio station. And            

559
00:28:13,525 --> 00:28:16,960
we always just use this         
default shared instance of it,  

560
00:28:17,028 --> 00:28:19,162
kind of like user default,      
remember that one?              

561
00:28:19,230 --> 00:28:22,565
We had userdefault.standard,    
we just used the shared one,    

562
00:28:22,634 --> 00:28:24,734
same thing here. So             

563
00:28:24,803 --> 00:28:28,138
this method to say you wanna    
listen is called addObserver.   

564
00:28:28,206 --> 00:28:31,608
You're essentially going to     
observe this radio station,     

565
00:28:31,677 --> 00:28:34,244
to listen to see if             
anything is broadcast           

566
00:28:34,312 --> 00:28:37,080
there. And you see it has       
a return value there, which is  

567
00:28:37,149 --> 00:28:40,851
of type NSObjectProtocol, I'm   
gonna cover that in a second.   

568
00:28:40,920 --> 00:28:43,653
But first let's look at         
the arguments to this thing.    

569
00:28:43,722 --> 00:28:46,656
First of all, we have forName,  
you see this, right, forName,   

570
00:28:46,725 --> 00:28:50,293
Notification.Name, that's the   
name of the radio station. And  

571
00:28:50,362 --> 00:28:52,629
notice it's type                
is not string,                  

572
00:28:52,697 --> 00:28:56,733
it's Notification.Name. And     
so if you, when you name it,    

573
00:28:56,801 --> 00:28:59,402
you will have to create your    
own Notification.Name if you    

574
00:28:59,471 --> 00:29:02,105
wanna broadcast on your own     
radio station. Which is fine,   

575
00:29:02,174 --> 00:29:05,142
you wanna give your radio       
station a unique name. But      

576
00:29:05,210 --> 00:29:08,278
if you wanna look and find      
the radio stations that exist   

577
00:29:08,347 --> 00:29:12,315
already in iOS, and there are   
dozens of them. iOS is very     

578
00:29:12,384 --> 00:29:14,618
good at broadcasting on         
a lot of radio stations.        

579
00:29:14,687 --> 00:29:16,153
You can just go look in         
the documentation for           

580
00:29:16,221 --> 00:29:18,721
Notification.Name, and you'll   
see them all listed there.      

581
00:29:18,790 --> 00:29:22,358
What they do, when they         
broadcast, that kind of stuff.  

582
00:29:22,427 --> 00:29:24,661
So that's why it's nice that    
they made it not a string,      

583
00:29:24,729 --> 00:29:27,664
but a type that you can go      
look up in the documentation.   

584
00:29:27,733 --> 00:29:30,700
All right, the next thing       
is this object Any?.            

585
00:29:30,769 --> 00:29:33,570
That is who's broadcasting      
on this radio station,          

586
00:29:33,639 --> 00:29:35,739
because unlike real             
radio stations,                 

587
00:29:35,808 --> 00:29:39,242
multiple people can broadcast   
on the same frequency,          

588
00:29:39,311 --> 00:29:42,178
and that's perfectly allowed.   
And this just says who          

589
00:29:42,247 --> 00:29:45,716
is broadcasting at the, who     
did the broadcast that you're   

590
00:29:45,784 --> 00:29:49,386
receiving when your closure     
gets called here. And           

591
00:29:49,454 --> 00:29:51,254
then you see right there,       
we have the queue,              

592
00:29:51,322 --> 00:29:54,391
this OperationQueue. That's     
what queue do you want your     

593
00:29:54,460 --> 00:29:58,462
closure to be executed on.      
Now, this can be nil, but       

594
00:29:58,530 --> 00:30:01,365
you almost never want nil.      
What nil means is,              

595
00:30:01,433 --> 00:30:07,804
execute my closure on the same  
queue as the broadcaster.       

596
00:30:07,873 --> 00:30:11,041
You do not want that usually,   
unless you're the broadcaster,  

597
00:30:11,109 --> 00:30:12,976
if it's your own code, and      
you're doing the broadcasting,  

598
00:30:13,045 --> 00:30:14,411
maybe you want that. But        

599
00:30:14,480 --> 00:30:15,979
if you're listening to          
something from iOS, for         

600
00:30:16,048 --> 00:30:18,548
example, no, you probably       
want the main queue. Now,       

601
00:30:18,616 --> 00:30:22,318
notice that says operation      
queue, not dispatch queue, and  

602
00:30:22,387 --> 00:30:24,521
I actually mentioned this when  
I talked about dispatch queue.  

603
00:30:24,590 --> 00:30:27,857
That there's an object          
oriented API to doing all that  

604
00:30:27,926 --> 00:30:31,061
dispatch stuff, called          
Operation and OperationQueue.   

605
00:30:31,129 --> 00:30:33,363
Well, this is using that        
object-oriented API,            

606
00:30:33,432 --> 00:30:34,431
if you want the main queue,     

607
00:30:34,500 --> 00:30:36,667
which is what you               
want 99% of the time,           

608
00:30:36,735 --> 00:30:39,336
just say OperationQueue.main.   
The same way you say            

609
00:30:39,404 --> 00:30:43,239
DispatchQueue.main, you can     
say OperationQueue.main. And    

610
00:30:43,308 --> 00:30:46,576
then the last argument to this  
addObserver is the closure you  

611
00:30:46,644 --> 00:30:49,046
want to execute. And that       
closure only has one argument,  

612
00:30:49,114 --> 00:30:52,548
which is a notification. A      
notification is just a little   

613
00:30:52,617 --> 00:30:55,786
object that has, for example,   
the name of the radio station   

614
00:30:55,854 --> 00:30:58,488
and who the broadcaster is.     
But it also has a very          

615
00:30:58,557 --> 00:31:01,224
important piece of              
information called userInfo.    

616
00:31:01,293 --> 00:31:05,162
userInfo is the music that's    
being broadcast to you,         

617
00:31:06,298 --> 00:31:07,163
it's almost always,             

618
00:31:07,232 --> 00:31:10,567
it's a type any, but it's       
almost always a dictionary.     

619
00:31:10,635 --> 00:31:13,136
And when you look in            
the documentation notification  

620
00:31:13,205 --> 00:31:14,871
name to find all                
the radio stations.             

621
00:31:14,940 --> 00:31:17,507
They will say,                  
when we broadcast,              

622
00:31:17,576 --> 00:31:21,110
we include the following        
keys in the dictionary, this    

623
00:31:21,179 --> 00:31:25,815
information. So that's a very   
important piece to understand,  

624
00:31:25,884 --> 00:31:28,418
is that your closure has this   
one argument, notification.     

625
00:31:28,486 --> 00:31:31,287
You look at the var userInfo    
in that notification to get     

626
00:31:31,356 --> 00:31:34,858
the music that's coming across  
the radio station right now,    

627
00:31:34,926 --> 00:31:37,160
all right? Now let's talk       
about that return value,        

628
00:31:37,229 --> 00:31:38,761
you see that                    
observer up there?              

629
00:31:38,830 --> 00:31:41,832
Notice that really weird type,  
NSObjectProtocol,               

630
00:31:41,900 --> 00:31:44,600
what the heck is                
NSObjectProtocol?               

631
00:31:44,669 --> 00:31:47,470
NSObjectProtocol is a protocol  
that NSObject happens to        

632
00:31:47,539 --> 00:31:51,074
implement. It's a subset of     
the functionality of NSObject   

633
00:31:51,143 --> 00:31:54,811
that some objects implement     
that aren't subclasses of       

634
00:31:54,880 --> 00:31:58,314
NSObject. So that, you know,    
this kind, this well-known      

635
00:31:58,383 --> 00:32:01,985
set of things. However, that's  
completely irrelevant here.     

636
00:32:02,054 --> 00:32:05,188
Does not matter. That thing     
might as well be in any as far  

637
00:32:05,257 --> 00:32:08,191
as you're concerned. All this   
thing, this observer thing is   

638
00:32:08,259 --> 00:32:12,395
a cookie that just keeps        
track, that basically this      

639
00:32:12,464 --> 00:32:15,431
observation is this thing.      
So, it's just a cookie for      

640
00:32:15,500 --> 00:32:18,668
you to hold on to.              
You only do one thing with it,  

641
00:32:18,737 --> 00:32:22,038
which is stop observing.        
It's how you say                

642
00:32:22,107 --> 00:32:25,242
I don't wanna listen to that    
radio station anymore. And      

643
00:32:25,310 --> 00:32:28,678
you do that by asking the       
NotificationCenter.default to   

644
00:32:28,747 --> 00:32:32,415
remove observer, this cookie.   
And it will stop listening. So  

645
00:32:32,484 --> 00:32:35,384
we'll show you an example       
of that in a second.            

646
00:32:35,453 --> 00:32:39,923
Quickly on Notification.Name,   
all of the notification names,  

647
00:32:39,992 --> 00:32:43,459
they collect them as static     
lets, little static let         

648
00:32:43,528 --> 00:32:48,131
constant Notification.Names in  
the Notification.Name class.    

649
00:32:48,200 --> 00:32:51,735
By the way, you'll often see    
it called NSNotification.Name.  

650
00:32:51,803 --> 00:32:52,802
That's the same thing.          

651
00:32:52,871 --> 00:32:55,771
They're literally type aliased  
to each other. You know,        

652
00:32:55,840 --> 00:32:57,941
in the Swift world, we would    
call it Notification.Name,      

653
00:32:58,009 --> 00:33:00,810
and in the Objective-C world,   
NSNotification.Name.            

654
00:33:00,879 --> 00:33:04,581
Fine, they're the same exact    
thing. And again, if you wanna  

655
00:33:04,650 --> 00:33:08,151
create your own radio station,  
we actually, or I recommend     

656
00:33:08,220 --> 00:33:11,254
creating an extension to        
Notification.Name, and          

657
00:33:11,323 --> 00:33:14,590
adding your own static let      
which is your thing, equals,    

658
00:33:14,659 --> 00:33:19,295
Notification.Name, of some      
string, any string you want.    

659
00:33:19,364 --> 00:33:21,898
That way you'll be collected    
in exactly the same             

660
00:33:21,967 --> 00:33:25,101
kind of API realm as all of     
the other notification names.   

661
00:33:25,170 --> 00:33:28,338
And you'll see that when we     
do the demo. All right, so      

662
00:33:28,407 --> 00:33:31,675
here's an example of listening  
to the radio station.           

663
00:33:31,743 --> 00:33:32,609
What's a good example?          

664
00:33:32,677 --> 00:33:34,410
This is a great example.        
Remember,                       

665
00:33:34,479 --> 00:33:37,080
the slider that said, set your  
font size, the accessibility    

666
00:33:37,148 --> 00:33:40,283
slider? You can make it bigger  
and smaller? Well, you can      

667
00:33:40,352 --> 00:33:43,786
find out, because there's       
a radio station broadcast       

668
00:33:43,855 --> 00:33:47,257
anytime that changes. So        
that's a great thing to know.   

669
00:33:47,325 --> 00:33:50,260
If you have something in your   
UI whose font is based on       

670
00:33:50,329 --> 00:33:53,697
that, for example, we talked    
about doing the cool thing of   

671
00:33:53,765 --> 00:33:56,632
having the collection view      
on the top of emoji art,        

672
00:33:56,701 --> 00:34:00,704
having its emoji get bigger or  
smaller, based on this slider.  

673
00:34:00,772 --> 00:34:02,472
Which would not be that         
hard to do. I'm not             

674
00:34:02,540 --> 00:34:05,308
gonna do it as a demo but       
you can do it as an exercise.   

675
00:34:05,376 --> 00:34:09,079
The main thing we would have    
to do is have our cell size     

676
00:34:09,148 --> 00:34:13,950
be, fixed to this font          
size by doing our               

677
00:34:14,019 --> 00:34:16,886
little font metric scaling.     
And we would also have to have  

678
00:34:16,955 --> 00:34:20,123
a layout constraint for the     
height of our collection view   

679
00:34:20,191 --> 00:34:23,159
that we wanna set in code to    
be the height of the cells.     

680
00:34:23,227 --> 00:34:26,062
Because remember that our       
cells can't be larger than our  

681
00:34:26,131 --> 00:34:28,698
collection view. So we'd have   
to make the collection view     

682
00:34:28,766 --> 00:34:31,168
bigger and the cells.           
But we could easily do that.    

683
00:34:31,236 --> 00:34:33,102
But if we did that,             
we would definitely want to be  

684
00:34:33,171 --> 00:34:34,537
listening to this               
radio station.                  

685
00:34:34,606 --> 00:34:36,772
Because every time              
that font changed,              

686
00:34:36,841 --> 00:34:40,143
we'd have to re-layout our      
collection view, of course,     

687
00:34:40,211 --> 00:34:42,278
all right? So here's            
what it would look like.        

688
00:34:42,347 --> 00:34:44,781
We get the                      
NotificationCenter.default.     

689
00:34:44,849 --> 00:34:47,884
We create this observer var     
which we set equal to doing     

690
00:34:47,953 --> 00:34:51,121
addObserver. The name of        
that radio station is           

691
00:34:51,189 --> 00:34:55,758
Notification.Name.UIContentSi-  
zeCategoryDidChange.            

692
00:34:55,827 --> 00:34:57,861
That's kind of a mouthful but   
that's what it is.              

693
00:34:57,929 --> 00:35:01,197
We're listening for that        
from UIApplication.shared.      

694
00:35:01,266 --> 00:35:03,432
That's the application object.  
I'm gonna talk about that at    

695
00:35:03,501 --> 00:35:06,636
the end of this lecture.        
You could also put nil there.   

696
00:35:06,705 --> 00:35:09,305
Cuz basically if anyone         
broadcasts that thing changed,  

697
00:35:09,374 --> 00:35:12,408
you're interested. So it would  
be fine to say nil here.        

698
00:35:12,477 --> 00:35:14,977
That means if anybody           
broadcasts it. And then of      

699
00:35:15,046 --> 00:35:18,548
course OperationQueue.main. I   
say or nil but really we would  

700
00:35:18,617 --> 00:35:21,484
want .main there. Cuz we're     
not actually sure what thread   

701
00:35:21,553 --> 00:35:23,720
this iOS would be               
broadcasting this on.           

702
00:35:23,788 --> 00:35:26,323
So we want to make sure we're   
on the main thread when we      

703
00:35:26,391 --> 00:35:30,160
do our stuff, and then our      
closure. Now inside our         

704
00:35:30,229 --> 00:35:33,196
closure we cause our            
collection view to redraw.      

705
00:35:33,265 --> 00:35:36,766
Whatever we do is fine.         
And also notice there,          

706
00:35:36,834 --> 00:35:39,135
there's something, some music   
broadcast on this station.      

707
00:35:39,204 --> 00:35:43,439
Which is, you can find out the  
content size category. And so   

708
00:35:43,508 --> 00:35:45,775
there's names for               
all those detentes,             

709
00:35:45,844 --> 00:35:50,213
in the slider there, like       
UIContentSizeCategorySmall,     

710
00:35:50,281 --> 00:35:54,517
UIContentSizeLarge,             
UIContentSizeCategoryAccessib-  

711
00:35:54,585 --> 00:35:56,452
ilityLarge, which               
is even larger.                 

712
00:35:56,521 --> 00:35:58,521
And there's like very large,    
and extra large, I don't know.  

713
00:35:58,590 --> 00:36:01,690
There's all kinds of different  
spots in there that you could   

714
00:36:01,759 --> 00:36:04,026
look at if you wanted to. But   
you're probably not going to.   

715
00:36:04,095 --> 00:36:06,596
You're probably in that         
collection example just going   

716
00:36:06,665 --> 00:36:08,731
to resize your font based       
on the font metrics.            

717
00:36:08,800 --> 00:36:11,434
Remember how we do that scaled  
font thing off the UI Metrics.  

718
00:36:11,502 --> 00:36:15,605
You would just cause that to    
recalculate, all right? Now,    

719
00:36:15,674 --> 00:36:19,375
notice that I hold on to var    
observer right there. And then  

720
00:36:19,444 --> 00:36:22,979
I remove it when I'm done. So,  
it is a good question here.     

721
00:36:23,048 --> 00:36:27,316
When do I add and when do I     
remove observing. Well, almost  

722
00:36:27,385 --> 00:36:29,886
always you're doing this as     
part of something you're doing  

723
00:36:29,954 --> 00:36:32,822
in the ViewController.          
So a perfect time and           

724
00:36:32,890 --> 00:36:36,392
probably 90% of the time,       
when you get viewWillAppear or  

725
00:36:36,461 --> 00:36:39,529
viewDidAppear, you              
add observer. And               

726
00:36:39,598 --> 00:36:42,398
then on viewWillDisappear or    
viewDidDisappear,               

727
00:36:42,467 --> 00:36:45,635
you remove the observer.        
That makes sense?               

728
00:36:45,704 --> 00:36:48,504
Because you're only interested  
in really getting these size    

729
00:36:48,573 --> 00:36:51,441
changes while                   
you're on-screen.               

730
00:36:51,509 --> 00:36:52,675
of course, the size might       
change while you're offscreen.  

731
00:36:52,676 --> 00:36:53,842
Now if you do that,             

732
00:36:53,912 --> 00:36:55,311
So when you get                 
viewWillAppear,                 

733
00:36:55,380 --> 00:36:57,780
you'll probably also wanna      
look at the size category,      

734
00:36:57,849 --> 00:36:59,782
which you can do.               
UIApplication has a var for     

735
00:36:59,851 --> 00:37:02,418
that. And adjust your           
collection view then            

736
00:37:02,487 --> 00:37:05,221
before you appear. But          
it's kinda a waste for you to   

737
00:37:05,290 --> 00:37:08,091
be listening to that thing all  
the time and changing things    

738
00:37:08,159 --> 00:37:10,359
when you're not even on         
screen. So viewWillAppear,      

739
00:37:10,428 --> 00:37:13,429
viewDidDisappear are great      
places to put add observer,     

740
00:37:13,498 --> 00:37:16,765
remove observer pairs. Always   
pair these things. Don't        

741
00:37:16,834 --> 00:37:22,605
forget to remove observer. How  
about broadcasting on your own  

742
00:37:22,674 --> 00:37:25,508
radio station. How do you       
do that? You do that with       

743
00:37:25,577 --> 00:37:27,577
the NotificationCenter.default  
as well.                        

744
00:37:27,646 --> 00:37:30,680
The method there is called      
post. The first argument,       

745
00:37:30,748 --> 00:37:32,715
the name, is the name           
of the radio station.           

746
00:37:32,784 --> 00:37:35,585
You get to make that up. We've  
talked about how to do that.    

747
00:37:35,654 --> 00:37:38,755
object, that's you. That's      
who's sending it. Usually       

748
00:37:38,823 --> 00:37:40,890
that's self. You can make that  
any object that you want.       

749
00:37:40,958 --> 00:37:43,393
But, that is who                
the NotificationCenter will     

750
00:37:43,461 --> 00:37:44,627
report as the sender,           

751
00:37:44,696 --> 00:37:48,197
the broadcaster.                
And then userInfo, that's       

752
00:37:48,266 --> 00:37:51,034
your music. And that's, almost  
always, you're gonna want to    

753
00:37:51,102 --> 00:37:53,502
put that as a dictionary        
of AnyHashable thing            

754
00:37:53,571 --> 00:37:56,639
to an Anys. So it's very        
flexible, you can put anything  

755
00:37:56,707 --> 00:38:00,510
you want in there. Now, as      
soon as you call this method,   

756
00:38:00,578 --> 00:38:04,648
it will immediately call        
all the closures for            

757
00:38:04,716 --> 00:38:07,683
that have addObserver           
to your radio station,          

758
00:38:07,752 --> 00:38:12,388
with a following caveat.        
It's only gonna immediately     

759
00:38:12,457 --> 00:38:15,357
call them If they               
specified queue nil.            

760
00:38:15,426 --> 00:38:17,960
Cuz then it's gonna execute     
their closures on the same      

761
00:38:18,029 --> 00:38:21,130
queue as this. So               
then it executes right away.    

762
00:38:21,198 --> 00:38:23,800
If they specified a different   
queue like the main queue,      

763
00:38:23,869 --> 00:38:27,069
then this is going to post      
their closures to execute.      

764
00:38:27,138 --> 00:38:29,405
And it will execute             
as soon as that                 

765
00:38:29,474 --> 00:38:33,175
queue gets around               
to their closure.               

766
00:38:33,244 --> 00:38:37,079
So that's notifications.        
All right, KVO. Now I'm gonna   

767
00:38:37,148 --> 00:38:39,949
spend two slides on this. But   
I wanna emphasize up front,     

768
00:38:40,018 --> 00:38:43,452
this is not a major important   
thing you're gonna do this.     

769
00:38:43,521 --> 00:38:46,656
Most quarters, I don't          
even talk about this. But       

770
00:38:46,724 --> 00:38:49,024
I kinda decided to throw        
it in this quarter just so      

771
00:38:49,093 --> 00:38:51,928
you can kinda know              
it exists out there.            

772
00:38:51,997 --> 00:38:54,630
It's not really a primary       
way of doing things.            

773
00:38:54,699 --> 00:38:57,032
Notification is much            
more of a primary way.          

774
00:38:57,101 --> 00:39:00,136
This much less primary.         
And it's because, it's because  

775
00:39:00,205 --> 00:39:03,506
it's kinda limited a little     
bit in its application.         

776
00:39:03,575 --> 00:39:07,576
So what is KVO? The basic idea  
here is, when it comes right    

777
00:39:07,645 --> 00:39:12,048
down to it, it's the idea of    
registering a closure that      

778
00:39:12,116 --> 00:39:16,619
gets executed when a property   
on a sub-class of NSObject      

779
00:39:16,688 --> 00:39:19,822
changes.                        
That's pretty much what it is.  

780
00:39:19,891 --> 00:39:23,826
Now let's talk about some of    
the caveats I just put there.   

781
00:39:23,895 --> 00:39:27,096
To make KVO work, you can't     
just have any property and      

782
00:39:27,164 --> 00:39:30,099
you change it and someone       
can register a closure.         

783
00:39:30,168 --> 00:39:32,369
Think about the overhead        
of doing that.                  

784
00:39:32,437 --> 00:39:33,903
You would not want that for     
every property.                 

785
00:39:33,972 --> 00:39:36,706
A lot of properties are         
probably they act as inlined    

786
00:39:36,774 --> 00:39:37,440
by the compiler.                

787
00:39:37,508 --> 00:39:40,309
So there's no way you would     
be able to do that. So          

788
00:39:40,378 --> 00:39:42,612
there's a mechanism that's      
required to do this.            

789
00:39:42,681 --> 00:39:45,414
Now NSObject, remember          
what NSObject is, right?        

790
00:39:45,483 --> 00:39:48,051
It's the root of all            
iOS classes, right? So          

791
00:39:48,119 --> 00:39:51,721
UIViewController, UIView, they  
all inherit from NSObject.      

792
00:39:51,790 --> 00:39:54,290
So NSObject puts                
this mechanism                  

793
00:39:54,359 --> 00:39:57,193
that makes it possibly to       
watch a property into it.       

794
00:39:57,261 --> 00:40:00,930
So that's why I say This is     
for subclasses of NSObject,     

795
00:40:00,998 --> 00:40:03,666
you could put this mechanism    
in your own object, however.    

796
00:40:03,735 --> 00:40:06,402
It's not that difficult,        
I'm not gonna cover it, but     

797
00:40:06,471 --> 00:40:09,372
people usually don't.           
They just use the mechanism of  

798
00:40:09,441 --> 00:40:12,808
using NSObject by having        
their thing, whatever it is,    

799
00:40:12,877 --> 00:40:15,745
their class,                    
subclass from NSObject. So      

800
00:40:15,814 --> 00:40:17,580
that's the first                
thing to understand.            

801
00:40:17,648 --> 00:40:19,716
There's kind of some mechanism  
there that you would have       

802
00:40:19,784 --> 00:40:21,851
to implement if you didn't      
wanna subclass NSObject.        

803
00:40:23,321 --> 00:40:26,255
What is this thing good for,    
what's KVO good for? Well,      

804
00:40:26,324 --> 00:40:28,724
it's kind of good for some the  
same things as notification.    

805
00:40:28,793 --> 00:40:31,427
Blind structured                
communication between things,   

806
00:40:31,496 --> 00:40:34,196
especially between models and   
their controllers.              

807
00:40:34,265 --> 00:40:36,365
But also between a view and     
their controller, or            

808
00:40:36,434 --> 00:40:38,534
even between a view and         
itself, as you'll see in        

809
00:40:38,603 --> 00:40:42,739
the demo here. Not every        
property works with KVO,        

810
00:40:42,808 --> 00:40:44,607
as I said,                      
that would be ridiculous. For   

811
00:40:44,676 --> 00:40:46,008
a property to work with it,     

812
00:40:46,077 --> 00:40:48,077
not only do you need            
the NSObject mechanism, but     

813
00:40:48,146 --> 00:40:51,480
the property has to be what's   
called key value coding         

814
00:40:51,549 --> 00:40:53,516
compliant. Now,                 
what that means is,             

815
00:40:53,585 --> 00:40:56,853
that property can be set        
by sending set value for        

816
00:40:56,921 --> 00:41:00,723
key, where the key is the key   
path of that property, and      

817
00:41:00,791 --> 00:41:02,892
get value for key to get it.    
In other words,                 

818
00:41:02,960 --> 00:41:05,895
there's these functions, set    
value for key and value for     

819
00:41:05,963 --> 00:41:08,831
key, that you can call to get   
the value of the property.      

820
00:41:08,900 --> 00:41:11,367
That has to be possible         
on the object,                  

821
00:41:11,436 --> 00:41:13,903
that has to work if             
you want do it. And             

822
00:41:13,972 --> 00:41:16,872
that's called key value         
compoding, key value coding     

823
00:41:16,941 --> 00:41:19,842
compliant. So that property     
has to be that way, now,        

824
00:41:19,910 --> 00:41:23,646
you have to do some work to     
make that happen. Properties    

825
00:41:23,714 --> 00:41:26,182
don't just magically make that  
work, you usually have to       

826
00:41:26,250 --> 00:41:28,717
implement something like value  
for key and set value for       

827
00:41:28,786 --> 00:41:31,887
key to make that work. Now,     
there are a few properties      

828
00:41:31,956 --> 00:41:36,559
scattered throughout iOS that   
are key value observing,        

829
00:41:36,628 --> 00:41:38,861
that work with key value        
observing. Most notably,        

830
00:41:38,930 --> 00:41:42,965
in UI view, center and          
frame are key value observing.  

831
00:41:43,033 --> 00:41:46,235
So you can observe the center   
or frame, and/or frame of       

832
00:41:46,304 --> 00:41:48,338
a view, and you can find        
out when it moves, so           

833
00:41:48,406 --> 00:41:52,007
that's kinda cool. Also,        
most of the properties in       

834
00:41:52,076 --> 00:41:55,077
the CALayer underneath UIView,  
remember the place where we     

835
00:41:55,146 --> 00:41:56,545
put the border                  
around the view,                

836
00:41:56,614 --> 00:41:58,648
back in assignment three or     
something like that?            

837
00:41:58,716 --> 00:42:02,618
That layer that's doing a lot   
of the drawing for UIView,      

838
00:42:02,687 --> 00:42:06,722
that layer is mostly key value  
observing compliant. So you     

839
00:42:06,791 --> 00:42:09,392
can observe things happening    
at that layer as well. And      

840
00:42:09,461 --> 00:42:11,393
they are scattering other       
places, for example,            

841
00:42:11,462 --> 00:42:15,398
core data. Remember core data,  
the object oriented database?   

842
00:42:15,466 --> 00:42:17,933
Key value observing can         
be really big there.            

843
00:42:18,002 --> 00:42:21,304
You could watch everything      
happening in your database      

844
00:42:21,372 --> 00:42:25,307
on a per-property basis by      
using key value observing. So   

845
00:42:25,376 --> 00:42:29,078
there are some frameworks that  
actually use KVO a lot. But     

846
00:42:29,147 --> 00:42:32,014
for the most part,              
we don't use it in the main     

847
00:42:32,083 --> 00:42:34,684
line that much. And of course,  
you could make your own         

848
00:42:34,752 --> 00:42:36,886
NSObject subclass that          
implements this stuff.          

849
00:42:36,954 --> 00:42:39,354
But that's way outside          
the scope of this class, and    

850
00:42:39,423 --> 00:42:42,258
again, template sizing is not,  
this is not that huge a deal.   

851
00:42:42,326 --> 00:42:45,394
All right, so how does that     
work, what is KVO look like?    

852
00:42:45,463 --> 00:42:48,497
There's this one very           
important method that NSObject  

853
00:42:48,566 --> 00:42:51,134
provides for you,               
called observe. So              

854
00:42:51,202 --> 00:42:54,570
observe takes a keyPath as      
an argument and a closure, and  

855
00:42:54,639 --> 00:42:58,240
it executes that closure        
whenever that keyPath changes.  

856
00:42:58,309 --> 00:43:01,477
Only works for keyPath that     
are key value compliant,        

857
00:43:01,545 --> 00:43:05,214
key value coding compliant.     
Notice that it returns          

858
00:43:05,283 --> 00:43:07,683
a little cookie,                
our observation,                

859
00:43:07,752 --> 00:43:09,918
you see that? It's a little     
different than a notification,  

860
00:43:09,987 --> 00:43:13,956
though, you never say, remove   
observer on that cookie.        

861
00:43:14,025 --> 00:43:17,159
Instead, when that cookie       
goes out of the heap,           

862
00:43:17,228 --> 00:43:20,262
it stops observing.             
So as long as you want this     

863
00:43:20,331 --> 00:43:23,265
observation closure to          
be observing that thing,        

864
00:43:23,334 --> 00:43:25,935
just keep that cookie in the    
heap. As soon as you let it go  

865
00:43:26,003 --> 00:43:30,339
out of the heap,                
it will stop observing. Now,    

866
00:43:30,408 --> 00:43:32,574
the arguments you see to        
your closure, of course,        

867
00:43:32,643 --> 00:43:35,377
you get the thing that's being  
observed, observed handed back  

868
00:43:35,446 --> 00:43:37,313
to you. You also get            
this thing change,              

869
00:43:37,382 --> 00:43:41,617
that change is of type          
NSKeyValueObservedChange. And   

870
00:43:41,685 --> 00:43:44,954
that's a little object that     
you can get the old value of    

871
00:43:45,022 --> 00:43:47,089
the thing, the new value        
of the thing that changed,      

872
00:43:47,158 --> 00:43:49,691
that kind of stuff. It just     
basically tells you about       

873
00:43:49,760 --> 00:43:51,059
the change that happened,       

874
00:43:51,128 --> 00:43:53,328
that caused your                
closure to get called.          

875
00:43:53,397 --> 00:43:57,199
This KeyPath argument is not a  
string, used to be in the old   

876
00:43:57,268 --> 00:44:01,003
days. Nowadays, it's actually   
a typed thing in Swift, and     

877
00:44:01,071 --> 00:44:04,806
it has special syntax, which    
is backslash, the type, dot,    

878
00:44:04,875 --> 00:44:09,645
the name of the property. Now,  
Swift will infer the type for   

879
00:44:09,714 --> 00:44:13,749
you, so we almost always say    
backslash dot the property. So  

880
00:44:13,818 --> 00:44:15,918
for example, if we want         
to observe the center or        

881
00:44:15,987 --> 00:44:21,523
frame of a view we would        
say observe \.frame.            

882
00:44:21,592 --> 00:44:26,295
and that will be observing      
the view's frame. All right,    

883
00:44:26,364 --> 00:44:28,530
so I have a demo of             
both of these things,           

884
00:44:28,599 --> 00:44:31,934
notifications and KVO, so       
let's take a look at these.     

885
00:44:32,003 --> 00:44:35,571
What I'm gonna do here is,      
remember after last lecture,    

886
00:44:35,639 --> 00:44:39,342
I said, we don't want to have   
a save button in EmojiArt.      

887
00:44:39,411 --> 00:44:40,209
We're gonna get rid of that,    

888
00:44:40,278 --> 00:44:42,144
there's no reason to have       
a save button. Really,          

889
00:44:42,212 --> 00:44:45,080
when we hit Save, we were       
just telling our UI document,   

890
00:44:45,149 --> 00:44:48,951
something changed, so           
you should autosave soon.       

891
00:44:49,019 --> 00:44:51,854
Really, what we want is to      
watch our EmojiArt view,        

892
00:44:51,923 --> 00:44:54,490
and whenever an emoji           
gets added or resized or        

893
00:44:54,559 --> 00:44:57,126
moved, we want to               
notify the controller.          

894
00:44:57,195 --> 00:44:59,628
So the controller can tell its  
document, something changed,    

895
00:44:59,697 --> 00:45:01,530
then we can just ditch          
the save button.                

896
00:45:01,599 --> 00:45:03,232
Well, after lecture last time,  

897
00:45:03,301 --> 00:45:05,267
I told you I was gonna          
do that, and I did.             

898
00:45:05,336 --> 00:45:09,004
So the stuff that's posted has  
this in there, and what I used  

899
00:45:09,073 --> 00:45:12,208
was delegation. And it did it   
specifically cuz I wanted you   

900
00:45:12,277 --> 00:45:14,910
to see what it looks like       
to make your own delegate.      

901
00:45:14,979 --> 00:45:16,779
You've been using               
scroll view's delegate,         

902
00:45:16,847 --> 00:45:19,448
table view's delegate,          
collective view's delegate.     

903
00:45:19,517 --> 00:45:22,585
I wanted you to see, wanted     
you to make your own delegate,  

904
00:45:22,654 --> 00:45:25,354
so I created                    
an EmojiArtViewDelegate, and    

905
00:45:25,423 --> 00:45:27,556
I'll briefly show you           
what I did there.               

906
00:45:27,625 --> 00:45:31,293
And so that's great, but        
today, what I'm gonna do is     

907
00:45:31,362 --> 00:45:34,663
use notifications instead.      
Because you can image,          

908
00:45:34,732 --> 00:45:36,332
anything that's happening       
with a delegate,                

909
00:45:36,401 --> 00:45:38,634
that's blind structure          
communication. Well, we can do  

910
00:45:38,702 --> 00:45:40,937
that with a notification just   
by having a radio station,      

911
00:45:41,005 --> 00:45:44,039
which is the EmojiArt view      
something changed radio         

912
00:45:44,108 --> 00:45:47,076
station. And a controller will  
just tune in, and every time    

913
00:45:47,145 --> 00:45:49,878
it hears a broadcast on that,   
it'll tell its UI document,     

914
00:45:49,947 --> 00:45:53,015
something changed, that's what  
I heard on the radio station.   

915
00:45:53,084 --> 00:45:55,751
And so that's what we'll        
do there, and then KVO,         

916
00:45:55,820 --> 00:45:57,552
there's a great                 
use of KVO here.                

917
00:45:57,621 --> 00:46:00,456
Which is, right now, I had to   
go down where my gestures are,  

918
00:46:00,524 --> 00:46:03,125
remember, I dragged in some     
gesture code. I had to go in    

919
00:46:03,193 --> 00:46:05,894
there, and for every time       
a gesture changed the position  

920
00:46:05,963 --> 00:46:08,697
of an emoji, I had to tell my   
delegate something changed,     

921
00:46:08,766 --> 00:46:11,433
tell me. So I had a lot of      
code in there for that, so      

922
00:46:11,502 --> 00:46:13,569
I'm just gonna rip              
all that code out.              

923
00:46:13,638 --> 00:46:16,606
And instead, I'm gonna observe  
the center of my emojis, and    

924
00:46:16,674 --> 00:46:19,241
when my emojis move, or         
even when they're resized,      

925
00:46:19,309 --> 00:46:22,077
because when they resize,       
they have to be repositioned,   

926
00:46:22,146 --> 00:46:24,546
right? Cuz they grow from       
the upper left corner,          

927
00:46:24,615 --> 00:46:26,248
so I have to keep               
repositioning, so               

928
00:46:26,317 --> 00:46:28,251
I'm setting the center again.   
So                              

929
00:46:28,319 --> 00:46:30,786
I'm just gonna observe that,    
and when that happens,          

930
00:46:30,855 --> 00:46:33,255
then I'll broadcast on          
my radio station. So            

931
00:46:33,324 --> 00:46:36,392
that'll collect that code into  
one place, and keep it from     

932
00:46:36,460 --> 00:46:40,729
being spread out through all    
over my code in a messy way.    

933
00:46:40,798 --> 00:46:43,832
But before we do that stuff,    
I'm going to do a simple        

934
00:46:43,901 --> 00:46:47,202
notification thing, which is    
I'm just going to observe       

935
00:46:47,271 --> 00:46:50,839
the state of my UI document     
changing. You know how our UI   

936
00:46:50,908 --> 00:46:53,976
document goes through these     
document states, normal,        

937
00:46:54,045 --> 00:46:57,580
closed, progress available      
when it's, say, reading and     

938
00:46:57,648 --> 00:47:00,749
writing, saving, error,         
remember all those states?      

939
00:47:00,818 --> 00:47:03,552
Well, we're gonna watch that    
happen, just to kinda get       

940
00:47:03,621 --> 00:47:07,690
a warm up on notifications, to  
see what that looks like. So    

941
00:47:07,759 --> 00:47:10,158
let's do that one,              
I'm gonna go up here,           

942
00:47:10,227 --> 00:47:13,729
here's viewWillAppear, right    
here, and close. Right, so      

943
00:47:13,798 --> 00:47:16,632
here's our document opening     
and closing up here. So         

944
00:47:16,700 --> 00:47:22,070
all I'm gonna do here is, when  
my document first appears,      

945
00:47:22,139 --> 00:47:26,342
I'm going to start watching my  
document. And it broadcasts on  

946
00:47:26,411 --> 00:47:29,779
a radio station that tells      
me when its state changed.      

947
00:47:29,847 --> 00:47:31,547
So what does that look like,    
well,                           

948
00:47:31,616 --> 00:47:33,849
again, i need to capture        
the return values.              

949
00:47:33,918 --> 00:47:36,985
So, i'm gonna call my           
documentObserver equals,        

950
00:47:37,054 --> 00:47:39,856
let's go ahead and              
make a var for that.            

951
00:47:39,924 --> 00:47:43,659
private var documentObserver,   
remember, it's                  

952
00:47:43,727 --> 00:47:47,863
an NSObjectProtocol, optional.  
Again, this is the cookie,      

953
00:47:47,932 --> 00:47:50,432
we never send a message         
to this, ever. We don't         

954
00:47:50,501 --> 00:47:54,369
even not know what messages it  
responds to. So we're gonna,    

955
00:47:54,438 --> 00:47:57,839
create this document            
observer here, I'm gonna do     

956
00:47:57,908 --> 00:48:01,743
NotificationCenter.default      
That's how we do all of our     

957
00:48:01,812 --> 00:48:06,382
stuff. And do addObserver, so   
here's addObserver forName,     

958
00:48:06,450 --> 00:48:08,817
make this a little              
easier to read,                 

959
00:48:08,886 --> 00:48:14,123
is what I want to do here.      
I wish they had                 

960
00:48:14,192 --> 00:48:17,726
a little command key I could    
do that would do this for me.   

961
00:48:17,795 --> 00:48:21,263
All right, so we're gonna       
listen to the document state    

962
00:48:21,332 --> 00:48:23,799
radio station. So we,           
let's find the name of it.      

963
00:48:23,867 --> 00:48:27,002
I'm just gonna type,            
Notification.Name., and         

964
00:48:27,071 --> 00:48:30,839
you're gonna see how many       
radio stations there are in     

965
00:48:30,908 --> 00:48:36,512
iOS. A lot, okay? And you       
can go look at all these and    

966
00:48:36,581 --> 00:48:39,115
what they broadcast and what    
music they play and all these   

967
00:48:39,183 --> 00:48:41,484
things. We've already talked    
about some of these things,     

968
00:48:41,552 --> 00:48:45,954
for example, keyboard. Here's   
a keyboard hide, DidHide,       

969
00:48:46,023 --> 00:48:50,793
will show. And then of course   
the content category size did   

970
00:48:50,862 --> 00:48:54,096
change thing, right?            
There's that there.             

971
00:48:54,165 --> 00:48:58,901
So, the one we want is          
UIDocumentStateChanged,         

972
00:48:58,970 --> 00:49:02,338
you see the first one there?    
So UIDocumentStateChanged, so   

973
00:49:02,407 --> 00:49:04,139
that's the radio station        
we want to listen to.           

974
00:49:04,208 --> 00:49:07,710
We're only interested in        
broadcast from our document.    

975
00:49:09,113 --> 00:49:11,247
That's the sender. That's       
who we want to broadcast.       

976
00:49:11,315 --> 00:49:16,218
We of course want to be on      
the main queue here. And        

977
00:49:16,286 --> 00:49:19,154
here's the closure that's       
gonna be executed when someone  

978
00:49:19,223 --> 00:49:21,690
broadcasts on that.             
Here's our notification. Now    

979
00:49:21,759 --> 00:49:24,259
this notification I think it    
actually does have some music   

980
00:49:24,328 --> 00:49:26,895
on there, which is probably     
the document state. But         

981
00:49:26,964 --> 00:49:29,031
I don't even need it cuz I've   
got my document right here.     

982
00:49:29,100 --> 00:49:32,534
So I'll just grab its state.    
I'm just gonna say              

983
00:49:32,603 --> 00:49:37,940
print.documentState changed     
to. And                         

984
00:49:38,008 --> 00:49:45,414
we'll say are                   
self.documentState. I actually  

985
00:49:45,482 --> 00:49:48,617
added a little extension to     
documentState right there so    

986
00:49:48,686 --> 00:49:51,553
that it would print it          
out nicely .normal.close,       

987
00:49:51,622 --> 00:49:54,222
those kind of things. Now       
anytime you start listening     

988
00:49:54,291 --> 00:49:56,826
on a radio station, you         
immediately have to think when  

989
00:49:56,894 --> 00:49:59,094
am I going to stop listening    
on this radio station?          

990
00:49:59,163 --> 00:50:02,297
Well, here I'm starting even    
before my document opens, but   

991
00:50:02,366 --> 00:50:05,800
I'm waiting until view will     
appear. So I'm going to stop,   

992
00:50:05,869 --> 00:50:07,903
I could stop in view            
will disappear or               

993
00:50:07,972 --> 00:50:08,770
view did disappear, but         

994
00:50:08,839 --> 00:50:10,672
I'm actually going to stop      
when my document is fully       

995
00:50:10,741 --> 00:50:12,374
closed.                         
Once it's fully closed,         

996
00:50:12,443 --> 00:50:15,277
I certainly don't want to       
be watching it anymore. So      

997
00:50:15,346 --> 00:50:18,313
let's go down here where we     
close. This is the close,       

998
00:50:18,382 --> 00:50:20,949
here is where we closing.       
Right now we don't use          

999
00:50:21,018 --> 00:50:25,387
the little success closure      
that happens when we close.     

1000
00:50:25,455 --> 00:50:30,326
But I'm going to star using     
it. Success in space,           

1001
00:50:30,394 --> 00:50:35,397
Return. And in here I'm         
going to remove observing       

1002
00:50:35,466 --> 00:50:39,435
this documentObserver.          
So I'm just going to say here,  

1003
00:50:39,503 --> 00:50:44,406
if I can let observer, server   
equal my documentObserver.      

1004
00:50:44,475 --> 00:50:48,710
Then I'm going to ask           
the NotificationCenter.default  

1005
00:50:48,779 --> 00:50:51,213
center to remove                
that observer.                  

1006
00:50:51,281 --> 00:50:57,085
In other words, stop observing  
that. Everybody cool            

1007
00:50:57,154 --> 00:51:00,755
with that? Everyone understand  
what I'm saying here, about     

1008
00:51:00,824 --> 00:51:05,393
this is the completion closer   
from closing the document? So   

1009
00:51:05,462 --> 00:51:07,897
once it's closed, that way      
we'll be able to observe it     

1010
00:51:07,965 --> 00:51:13,736
closing. It will be nice.       
So let's go run this and        

1011
00:51:13,804 --> 00:51:16,438
watch our console, so I got     
my console going down here.     

1012
00:51:16,507 --> 00:51:20,209
Actually, this is my console    
over here. All right, so        

1013
00:51:20,278 --> 00:51:26,581
let's run. All right, so        
here's our app. So we           

1014
00:51:26,650 --> 00:51:28,684
haven't opened any documents.   
So we have nothing on here.     

1015
00:51:28,752 --> 00:51:32,621
I'm gonna go ahead and          
clear out my console.           

1016
00:51:32,689 --> 00:51:34,022
So we haven't opened            
any documents.                  

1017
00:51:34,091 --> 00:51:35,724
So we haven't gotten any        
documents to exchange.          

1018
00:51:35,792 --> 00:51:38,860
So I'm gonna open our Apple     
Bees. Here is our Apple Bee.    

1019
00:51:38,929 --> 00:51:42,230
And look, documentState date    
changed to normal, right?       

1020
00:51:42,299 --> 00:51:43,565
Because we opened               
the document,                   

1021
00:51:43,634 --> 00:51:47,102
now it's in normal. Now,        
how about putting something in  

1022
00:51:47,171 --> 00:51:50,539
here maybe an apple, something  
like that. Now it's, where,     

1023
00:51:50,608 --> 00:51:53,809
what's going to happen to the   
state right now? Okay well,     

1024
00:51:53,878 --> 00:51:56,211
eventually it's going to        
autosave. It does it about,     

1025
00:51:56,280 --> 00:51:58,580
I don't know, once a minute or  
something like that. But        

1026
00:51:58,649 --> 00:52:01,082
when it autosaves, we're going  
to notice because it's going    

1027
00:52:01,151 --> 00:52:04,787
to go to state progress         
available. There it is,         

1028
00:52:04,855 --> 00:52:07,489
progress available and          
then back to normal. Because    

1029
00:52:07,557 --> 00:52:09,358
the progress is available       
because it's saving and         

1030
00:52:09,426 --> 00:52:12,327
it can tell you the progress    
as it saves, and                

1031
00:52:12,396 --> 00:52:16,031
then goes back to normal. I'll  
show you another trick. Here,   

1032
00:52:16,100 --> 00:52:20,869
you can force an autosave,      
by the way, by threatening      

1033
00:52:20,937 --> 00:52:24,707
to switch to another app.       
Watch this, I'm going to drag   

1034
00:52:24,775 --> 00:52:27,175
up from the bottom like, I'm    
gonna switch to another app.    

1035
00:52:27,244 --> 00:52:30,512
This caused an autosave. Now,   
it didn't do it here because    

1036
00:52:30,581 --> 00:52:32,514
we haven't made any changes.    
But this is a great way         

1037
00:52:32,583 --> 00:52:35,150
to make sure that you're        
changing stuff works.           

1038
00:52:35,218 --> 00:52:38,787
So watch this, now I'm          
gonna add a something here.     

1039
00:52:38,856 --> 00:52:42,257
Now when I do this threat,      
whoop,                          

1040
00:52:42,326 --> 00:52:46,828
it's saved. See what happened   
there? So when you threaten to  

1041
00:52:46,897 --> 00:52:48,797
switch to another app           
autosave will auto save.        

1042
00:52:48,866 --> 00:52:51,033
Cuz it's just afraid, my gosh,  
I might get killed or           

1043
00:52:51,101 --> 00:52:53,101
who knows what,                 
I better save. So               

1044
00:52:53,170 --> 00:52:56,605
that's a nice trick to          
know when to do that. And       

1045
00:52:56,673 --> 00:53:01,310
if we close this then we get    
state changed to closed. So     

1046
00:53:01,379 --> 00:53:03,012
this is cool. We just listened  
to that radio station,          

1047
00:53:03,080 --> 00:53:04,913
we're just reporting            
what happened.                  

1048
00:53:04,982 --> 00:53:07,649
All right,                      
now let's go ahead and          

1049
00:53:07,718 --> 00:53:10,952
have our emoji artview          
be a broadcaster.               

1050
00:53:11,021 --> 00:53:15,257
We are listening to UIDocument  
which is the broadcaster here   

1051
00:53:15,326 --> 00:53:17,993
and we are the subscriber       
to the radio station.           

1052
00:53:18,062 --> 00:53:19,728
Now let's go the other way,     
let's have a broadcast.         

1053
00:53:19,797 --> 00:53:22,698
So I'm gonna go over to         
EmojiArt, and what I'm gonna    

1054
00:53:22,766 --> 00:53:25,133
do is every where I was         
doing my delegation,            

1055
00:53:25,202 --> 00:53:28,570
I'm going to use notification   
instead. So let's first review  

1056
00:53:28,639 --> 00:53:32,274
what I did after last lecture   
to implement delegation.        

1057
00:53:32,343 --> 00:53:36,378
All right, now, just like       
UIScrollView, UITableView,      

1058
00:53:36,446 --> 00:53:39,848
etc, I had to add               
a protocol for delegation.      

1059
00:53:39,917 --> 00:53:41,683
Now my delegation               
protocol it's called            

1060
00:53:41,752 --> 00:53:45,487
EmojiArtViewDelegate only has   
one function in it which is     

1061
00:53:45,556 --> 00:53:48,256
emojiArtViewChanged. Of course  
ScrollView has a whole bunch    

1062
00:53:48,325 --> 00:53:51,326
of them. DidScroll, view for    
zooming at, table views         

1063
00:53:51,395 --> 00:53:54,897
delegate has a lot of things.   
Height of row at, all these     

1064
00:53:54,965 --> 00:53:58,199
other things. We only have      
one, just this one. Now notice  

1065
00:53:58,268 --> 00:54:02,370
I made this restricted to only  
being implemented by classes.   

1066
00:54:02,439 --> 00:54:06,374
Why did I do that? Because      
the delegate method, or var,    

1067
00:54:06,443 --> 00:54:11,013
the delegate var in my view, I  
wanted it to be weak. And for   

1068
00:54:11,081 --> 00:54:13,748
it to be weak, it has to        
be able to be in the heap,      

1069
00:54:13,817 --> 00:54:15,317
and then get released and       

1070
00:54:15,386 --> 00:54:18,720
set to nil, when no one else    
is interested in it. Why did I  

1071
00:54:18,789 --> 00:54:22,557
make that weak? Well, imagine   
here that my controller sets    

1072
00:54:22,626 --> 00:54:26,361
itself as the delegate, which   
is likely. Very, very likely.   

1073
00:54:26,430 --> 00:54:29,765
If that happened,               
now we'd have a memory cycle    

1074
00:54:29,834 --> 00:54:32,100
because my view would be        
pointing to the controller.     

1075
00:54:32,168 --> 00:54:34,702
And of course, the controller   
points to all of its view.      

1076
00:54:34,771 --> 00:54:36,204
So now they are pointing        
to each other.                  

1077
00:54:36,273 --> 00:54:38,006
They are going to keep          
each other in the heap.         

1078
00:54:38,075 --> 00:54:40,208
By making this delegate weak,   
it makes so                     

1079
00:54:40,277 --> 00:54:43,578
that's no longer                
going to happen.                

1080
00:54:43,647 --> 00:54:45,914
So there's not a memory cycle   
because the view is not         

1081
00:54:45,983 --> 00:54:48,817
keeping the controller in       
memory cuz this is a weak       

1082
00:54:48,886 --> 00:54:52,254
pointer to it. So I added       
this var, this weak var, so     

1083
00:54:52,323 --> 00:54:54,789
now anybody who wants to know   
if I've changed can just set    

1084
00:54:54,858 --> 00:54:56,958
themselves as the delegate and  
of course the controller is     

1085
00:54:57,027 --> 00:55:02,730
going to do that. Then, every   
time I changed like right down  

1086
00:55:02,799 --> 00:55:07,102
here. I just sent this message  
to my delegate if I have one.   

1087
00:55:07,171 --> 00:55:09,905
My delegate could be nil, I     
don't have to have a delegate.  

1088
00:55:09,973 --> 00:55:10,672
And I just send it and          

1089
00:55:10,741 --> 00:55:13,575
of course I'm the sender,       
right? Delegate methods, we     

1090
00:55:13,644 --> 00:55:16,444
all will send ourselves along   
as the first argument. Do you   

1091
00:55:16,513 --> 00:55:18,179
know? You've noticed that       
I'm sure with ScrollView and    

1092
00:55:18,248 --> 00:55:20,415
TabelView and collection.       
They always send themselves,    

1093
00:55:20,484 --> 00:55:24,319
it's just convenience sake so   
that you have it right there.   

1094
00:55:24,388 --> 00:55:26,788
So I do that as well. Now       
this is not the only change,    

1095
00:55:26,857 --> 00:55:29,390
this is one I'm dropping.       
Of course, if I drop a new      

1096
00:55:29,459 --> 00:55:32,694
emoji in, that's a change, but  
I also had to go over here to   

1097
00:55:32,763 --> 00:55:34,730
gestures. And this is what      
I was talking about before,     

1098
00:55:34,798 --> 00:55:35,731
it's kind of annoying           

1099
00:55:35,799 --> 00:55:39,033
like when I select and move     
a view. I had to say, well,     

1100
00:55:39,102 --> 00:55:42,137
if this is the end of this      
gesture then send it.           

1101
00:55:42,205 --> 00:55:45,274
And also down here where I      
resized. I had to go and say,   

1102
00:55:45,342 --> 00:55:47,009
well, if it's the end           
of resizing, send it.           

1103
00:55:47,077 --> 00:55:48,577
Now I want to get               
rid of these and                

1104
00:55:48,645 --> 00:55:51,179
I'm going to be able to with    
KVO, but we'll leave them in    

1105
00:55:51,248 --> 00:55:55,551
there for now. So that's        
delegation. That's all that's   

1106
00:55:55,619 --> 00:55:58,754
necessary on this view side.    
Then on the controller side,    

1107
00:55:58,822 --> 00:56:02,891
what I did was when I created   
my emojiArtView down here,      

1108
00:56:02,960 --> 00:56:05,627
I set myself as its delegate.   

1109
00:56:05,695 --> 00:56:07,729
Well, if I'm gonna              
be its delegate,                

1110
00:56:07,798 --> 00:56:11,166
that means I have to implement  
the EmojiArtViewDelegate just   

1111
00:56:11,235 --> 00:56:13,968
like those implementing         
scrollviews delegate.           

1112
00:56:14,037 --> 00:56:16,638
And that means I have to        
actually implement that which   

1113
00:56:16,707 --> 00:56:19,174
is right here in my             
emojiArtViewDelegate methods    

1114
00:56:19,243 --> 00:56:22,844
implemented, and what did I     
do? I called documentChanged,   

1115
00:56:22,912 --> 00:56:26,815
and what is document changed?   
Here is document changed,       

1116
00:56:26,884 --> 00:56:30,118
it's the method                 
formerly known as Save.         

1117
00:56:30,187 --> 00:56:32,621
Cuz I ditched my Save           
button when I did this and      

1118
00:56:32,689 --> 00:56:35,324
just called and Save. These     
contents up here is exactly     

1119
00:56:35,392 --> 00:56:37,492
the same as it used to be.      
Just update my documents        

1120
00:56:37,561 --> 00:56:39,994
model to be my model and then   
update the documents changed    

1121
00:56:40,063 --> 00:56:43,298
count. It's all I do here.      
So that's delegation,           

1122
00:56:43,367 --> 00:56:45,467
that's the entirety of it.      
You see how it all works?       

1123
00:56:45,535 --> 00:56:47,769
Quite simple, and               
we're not gonna,                

1124
00:56:47,838 --> 00:56:50,706
we're not use delegation        
anymore in this.                

1125
00:56:50,774 --> 00:56:52,674
We're gonna leave               
delegation in the view but      

1126
00:56:52,743 --> 00:56:54,576
we're not gonna use             
it in our controller.           

1127
00:56:54,645 --> 00:56:55,844
Instead, we're gonna            
use a radio station.            

1128
00:56:55,912 --> 00:56:57,779
So let's go back                
to our artview and              

1129
00:56:57,848 --> 00:57:00,315
broadcast on a radio station.   
And I'm just gonna do           

1130
00:57:00,383 --> 00:57:02,250
it everywhere where I was       
talking to my delegate.         

1131
00:57:02,319 --> 00:57:04,652
Instead, I'm gonna broadcast    
on a radio station.             

1132
00:57:04,721 --> 00:57:08,223
I'm just gonna say              
NotificationCenter.default.p-   

1133
00:57:08,292 --> 00:57:10,358
ost, that's how we broadcast.   

1134
00:57:10,427 --> 00:57:14,395
And I have to give it a name    
and who is broadcasting. Well,  

1135
00:57:14,464 --> 00:57:17,232
who is broadcasting is me,      
and what are we gonna do for    

1136
00:57:17,300 --> 00:57:22,304
a name? Well, as I suggested,   
I recommend going here and      

1137
00:57:22,372 --> 00:57:26,641
doing an extension to           
notification.name and           

1138
00:57:26,710 --> 00:57:31,613
add your own static let         
which I'll call EmojiArtView    

1139
00:57:31,681 --> 00:57:35,617
did change notification and     
set it equal to                 

1140
00:57:35,686 --> 00:57:40,856
a notification.name with any    
string you want in here.        

1141
00:57:40,924 --> 00:57:42,824
I'll probably just use          
the same string here.           

1142
00:57:42,893 --> 00:57:45,460
It doesn't have to be the same  
string but I will, and          

1143
00:57:45,529 --> 00:57:46,628
this will now make it so        

1144
00:57:46,697 --> 00:57:48,964
you can do                      
notification.name.emojiartvie-  

1145
00:57:49,032 --> 00:57:51,967
wdidchange. That's the name     
of our radio station.           

1146
00:57:52,035 --> 00:57:55,003
Remember radio stations         
are Notification.Names, so      

1147
00:57:55,071 --> 00:57:59,107
this is that. So now,           
I can go down here and          

1148
00:57:59,176 --> 00:58:05,947
say I want my name to be        
Notification.Name.EmojiArtVie-  

1149
00:58:06,016 --> 00:58:12,253
wDidChange. And by the way, of  
course, Swift can infer this.   

1150
00:58:12,322 --> 00:58:15,056
So we can just go like that,    
which is what we would do, and  

1151
00:58:15,125 --> 00:58:17,459
type all of that in             
Notification.Name stuff for     

1152
00:58:17,527 --> 00:58:20,328
no good reason. And this is     
it, so that's all we need to    

1153
00:58:20,397 --> 00:58:22,864
do is do this. Now of course,   
we need to do it here,          

1154
00:58:22,933 --> 00:58:25,333
but we have to go again         
over to gestures over here.     

1155
00:58:25,402 --> 00:58:29,204
And do it in the same place we  
do this delegate right here,,   

1156
00:58:29,273 --> 00:58:31,406
where's this other              
one up here?                    

1157
00:58:31,475 --> 00:58:33,341
Okay so, again,                 
that's kind of annoying,        

1158
00:58:33,410 --> 00:58:35,844
we'll fix that with KVO. But    
right now, we're broadcasting   

1159
00:58:35,913 --> 00:58:37,846
on this radio station every     
time something changes.         

1160
00:58:37,915 --> 00:58:40,415
We resize something, we drop    
something, and whatever.        

1161
00:58:40,484 --> 00:58:42,583
Now, back over here             
in our controller,              

1162
00:58:42,652 --> 00:58:44,619
I'm no longer going             
to be a delegate.               

1163
00:58:44,687 --> 00:58:47,255
So I'm gonna go down here and   
just get rid of all this.       

1164
00:58:47,323 --> 00:58:50,492
So I'm not longer gonna set     
myself as the delegate here.    

1165
00:58:50,560 --> 00:58:54,496
Get rid of this entirely,       
I'm no longer gonna implement   

1166
00:58:54,565 --> 00:58:58,566
the EmojiArtView delegate. I'm  
no longer going to say that     

1167
00:58:58,635 --> 00:59:01,202
I implement                     
the EmojiartView delegate.      

1168
00:59:01,271 --> 00:59:04,072
So, now I've disconnected       
myself from my view.            

1169
00:59:04,141 --> 00:59:06,942
So instead, I'm gonna listen    
to that radio station, so       

1170
00:59:07,010 --> 00:59:10,212
where am I gonna do that? That  
one, let's start listening      

1171
00:59:10,280 --> 00:59:13,548
once the document's open.       
Until the document's open it's  

1172
00:59:13,616 --> 00:59:16,651
gonna be useless to listen to   
my emojiArtview. So again,      

1173
00:59:16,720 --> 00:59:20,054
I'm gonna need another          
little observer guy here.       

1174
00:59:20,123 --> 00:59:23,491
So I'm gonna call this one      
my emojiArtviewObserver cuz     

1175
00:59:23,560 --> 00:59:27,062
that's what its gonna be        
observing, the emojiArtview.    

1176
00:59:27,131 --> 00:59:30,332
I'm gonna say                   
emojiArtViewObserver, go,       

1177
00:59:30,401 --> 00:59:35,369
'm inside a closure here, cuz   
this is the completion closure  

1178
00:59:35,438 --> 00:59:40,943
of opening. So I'm gonna say    
self.emojiArtViewObserver       

1179
00:59:41,011 --> 00:59:45,280
= NotificationCenter,           
that's how we listen.           

1180
00:59:45,349 --> 00:59:50,218
Default.addObserver, same       
way as we add observer for      

1181
00:59:50,287 --> 00:59:55,157
the UIDocumentState.            
Let's sort this out again,      

1182
00:59:55,225 --> 00:59:59,761
so we can see this all real     
clearly. All right, so          

1183
00:59:59,830 --> 01:00:05,300
the name is                     
notification.Name.EmojiArtVie-  

1184
01:00:05,369 --> 01:00:09,937
wDidChange. And again,          
we don't need that just I was   

1185
01:00:10,006 --> 01:00:13,107
doing that so we would see      
it clearly. The object is my    

1186
01:00:13,176 --> 01:00:17,612
EmojiArtView, that's the only   
one I'm interested in hearing   

1187
01:00:17,681 --> 01:00:20,815
about emojiArt,                 
you did change broadcast.       

1188
01:00:20,884 --> 01:00:25,620
The Queue, of course operation  
Queue.Mean because I'm just,    

1189
01:00:25,688 --> 01:00:29,858
although surprisingly this      
would not need to be on main.   

1190
01:00:29,927 --> 01:00:32,627
Because all I'm gonna           
do is tell my document,         

1191
01:00:32,696 --> 01:00:35,797
which is part of my model,      
extended part of my model.      

1192
01:00:35,865 --> 01:00:39,167
I'm just gonna tell that it     
changed. That's not anything    

1193
01:00:39,235 --> 01:00:42,304
UI, so I don't necessarily      
have to do that here. I could   

1194
01:00:42,372 --> 01:00:45,473
put nil here and be pretty      
safe no matter what thread I'm  

1195
01:00:45,542 --> 01:00:48,776
broadcasting on. Now I happen   
to know that my emojiArtView    

1196
01:00:48,845 --> 01:00:51,913
is broadcasting from the main   
thread, right? Because it did   

1197
01:00:51,982 --> 01:00:54,115
it when it dropped or           
when someone resized, clearly,  

1198
01:00:54,184 --> 01:00:57,952
I'm on the main queue there.    
So it wouldn't matter but,      

1199
01:00:58,021 --> 01:01:00,155
anyway. Okay so here we go,     

1200
01:01:00,224 --> 01:01:03,124
now we do get this              
notification. Turns out that    

1201
01:01:03,193 --> 01:01:07,128
our EmojiArtView does not play  
any music when it broadcasts.   

1202
01:01:07,197 --> 01:01:10,031
It could, it could maybe send   
you the label that it added or  

1203
01:01:10,099 --> 01:01:12,567
changed or something.           
But it doesn't, that's okay.    

1204
01:01:12,636 --> 01:01:16,671
We don't care, because all we   
wanna know is that something    

1205
01:01:16,740 --> 01:01:20,575
changed so we can say           
documentChanged, right? That's  

1206
01:01:20,644 --> 01:01:24,446
it, now, of course, we need     
to stop listening to this.      

1207
01:01:24,515 --> 01:01:26,047
When is a good                  
time to do that?                

1208
01:01:26,116 --> 01:01:28,516
I'm gonna do that               
when you hit close.             

1209
01:01:28,585 --> 01:01:31,152
And I'm gonna do it whether or  
not you successfully closed     

1210
01:01:31,221 --> 01:01:33,254
because I'm gonna               
get dismissed. So               

1211
01:01:33,323 --> 01:01:35,624
I'm gonna most definitely       
stop listening here.            

1212
01:01:35,692 --> 01:01:40,028
And I'm just gonna say          
if I can let observer,          

1213
01:01:40,096 --> 01:01:46,200
observer = my emojiArt.View     
observer, art view observer.    

1214
01:01:46,269 --> 01:01:50,439
Then I'm gonna ask              
the notification center,        

1215
01:01:50,507 --> 01:01:55,310
the default one,                
to remove that observer. And    

1216
01:01:55,379 --> 01:01:58,513
that's it, so this is quite     
a bit simpler than delegation,  

1217
01:01:58,581 --> 01:02:00,648
on both sides. I's              
a little easier to do this.     

1218
01:02:00,717 --> 01:02:02,050
You don't have to implement     
that another method.            

1219
01:02:02,118 --> 01:02:03,218
You don't have to set           
yourself to delegate.           

1220
01:02:03,287 --> 01:02:03,985
You do't have to do that.       

1221
01:02:04,054 --> 01:02:06,020
You just start listening and    
stop listening and              

1222
01:02:06,089 --> 01:02:09,023
you're going to find out. So    
that's why we use notification  

1223
01:02:09,092 --> 01:02:11,726
a lot of times in place         
where other times we've used    

1224
01:02:11,794 --> 01:02:14,662
delegation and it's true        
in other classes, as well.      

1225
01:02:14,731 --> 01:02:17,399
All right, so let's go see if   
we broke anything. Cross our    

1226
01:02:17,467 --> 01:02:20,167
fingers that removing           
delegation entirely from our    

1227
01:02:20,236 --> 01:02:23,371
mode emoji.Art.ViewController   
did not break anything.         

1228
01:02:23,440 --> 01:02:25,440
And luckily, we have that       
other observing going on, so    

1229
01:02:25,509 --> 01:02:27,709
we'll be able to tell.          
So here's apple bee,            

1230
01:02:27,777 --> 01:02:31,412
let's bring up our Console      
there, change to normal,        

1231
01:02:31,481 --> 01:02:34,582
that's good. Now, hopefully     
when we drop something in,      

1232
01:02:34,651 --> 01:02:37,251
hopefully, that caused          
the radio station broadcast to  

1233
01:02:37,320 --> 01:02:39,654
happen so that we notice        
something is different.         

1234
01:02:39,723 --> 01:02:43,058
And hopefully, this is going    
to auto save in a moment,       

1235
01:02:43,126 --> 01:02:45,727
and we can force the issue      
by threatening to               

1236
01:02:45,795 --> 01:02:49,831
go somewhere else. Woo, it      
did it. So, it must have been   

1237
01:02:49,900 --> 01:02:53,000
that our radio station worked.  
And we noticed that change,     

1238
01:02:53,069 --> 01:02:56,637
otherwise we wouldn't have      
auto saved there. Okay          

1239
01:02:56,706 --> 01:03:00,308
the last thing we're gonna do   
is use KVO to rip out some of   

1240
01:03:00,376 --> 01:03:04,111
that code that's calling the    
delegate and posting down in    

1241
01:03:04,180 --> 01:03:07,615
my gesture view. Basically      
what I wanna do is go           

1242
01:03:07,683 --> 01:03:12,053
to my gestures right here,      
and I wanna remove this code.   

1243
01:03:12,121 --> 01:03:14,822
See, this is the code where     
I'm telling my delegate and     

1244
01:03:14,891 --> 01:03:17,259
posting on the radio            
station when, in this case,     

1245
01:03:17,327 --> 01:03:19,760
something moved.                
So I want that out of there,    

1246
01:03:19,829 --> 01:03:23,198
and then down here for resize,  
this is when we resize,         

1247
01:03:23,266 --> 01:03:26,434
I want this out of there.       
So I'm just gonna delete that.  

1248
01:03:26,503 --> 01:03:31,139
But I obviously, still need     
to tell people when I change.   

1249
01:03:31,207 --> 01:03:34,809
So I'm gonna go back to my      
ArtView here. And as soon as I  

1250
01:03:34,877 --> 01:03:38,813
add a label, I'm going to have  
that label be observed for      

1251
01:03:38,882 --> 01:03:42,217
its center changing. And if     
its center changes, I'm going   

1252
01:03:42,285 --> 01:03:44,952
to notify my delegate and       
broadcast on my radio station.  

1253
01:03:45,021 --> 01:03:47,221
'm basically gonna              
do this right here.             

1254
01:03:47,290 --> 01:03:50,325
So how do we do that? The       
trickiest thing about, this,    

1255
01:03:50,394 --> 01:03:54,562
it's actually quite easy.       
We're just gonna to label       

1256
01:03:54,631 --> 01:03:58,466
observe, and                    

1257
01:03:58,534 --> 01:04:03,738
what property observing /.      
Center.                         

1258
01:04:05,609 --> 01:04:08,309
And when we observe, we get     
a closure. The closure's gonna  

1259
01:04:08,378 --> 01:04:13,247
pass the label back to us, and  
that little changed object,     

1260
01:04:13,316 --> 01:04:15,917
right there. And we can do      
whatever we want in here.       

1261
01:04:15,986 --> 01:04:18,619
And what do we want to do?      
We want to do this.             

1262
01:04:18,688 --> 01:04:23,358
Tell our delegate and tell      
the radio station something     

1263
01:04:23,427 --> 01:04:27,528
changed. But remember observed  
returns a cookie. And           

1264
01:04:27,597 --> 01:04:30,698
we have to keep that cookie in  
the heap as long as we want     

1265
01:04:30,767 --> 01:04:33,534
this to happen. So I'm gonna    
do that by having a little      

1266
01:04:33,603 --> 01:04:38,306
private var which I'm gonna     
call my labelObservations.      

1267
01:04:38,375 --> 01:04:43,711
Which is gonna be a dictionary  
with UIViews as the keys and    

1268
01:04:43,780 --> 01:04:49,851
these NSKeyValueObservations    
as the values. Now putting      

1269
01:04:49,920 --> 01:04:53,221
things in this dictionary is    
gonna keep things in the heap.  

1270
01:04:53,290 --> 01:04:56,291
But only as long as this        
EmojiArtView is in the heap.    

1271
01:04:56,359 --> 01:04:58,259
As soon as this EmojiArtView    
leaves the heap                 

1272
01:04:58,328 --> 01:05:00,328
this will leave the heap and    
all the observations            

1273
01:05:00,397 --> 01:05:03,197
will leave the heap, woo-hoo.   
So that's what's great about    

1274
01:05:03,266 --> 01:05:05,099
this, not having to do          
that remote observe,            

1275
01:05:05,168 --> 01:05:07,969
remove observer thing like you  
do with notifications. Because  

1276
01:05:08,038 --> 01:05:10,437
when things leave the heap      
naturally the observations      

1277
01:05:10,506 --> 01:05:15,176
naturally stop. However, what   
if we don't leave the heap and  

1278
01:05:15,245 --> 01:05:18,312
we remove that subview.         
We don't have any,              

1279
01:05:18,381 --> 01:05:21,415
actually have any UI            
to remove our emojis.           

1280
01:05:21,484 --> 01:05:23,451
They once they're in there,     
they're there forever. But      

1281
01:05:23,519 --> 01:05:26,120
we could imagine putting some   
sort of gesture that would      

1282
01:05:26,189 --> 01:05:29,157
remove them, so we wanna        
anticipate that day and         

1283
01:05:29,226 --> 01:05:32,193
I wanna make sure we remove     
it. So, first of all let's put  

1284
01:05:32,262 --> 01:05:35,529
the observation,                
KeyValueObservations in here.   

1285
01:05:35,598 --> 01:05:40,301
I'm gonna say                   
labelObservations               

1286
01:05:40,369 --> 01:05:45,240
sub the label =                 
this observation.               

1287
01:05:45,308 --> 01:05:50,145
So this the labelObservation    
for this label, right. Now I    

1288
01:05:50,213 --> 01:05:54,549
have to whenever this view      
gets removed from super view,   

1289
01:05:54,618 --> 01:05:58,152
I have to let this              
observation leave the heap.     

1290
01:05:58,221 --> 01:06:00,221
In other words, I will have     
to remove it from here.         

1291
01:06:00,290 --> 01:06:02,657
Everyone understand that?       
So how do I do that?            

1292
01:06:02,726 --> 01:06:06,494
Well, luckily, there is         
a nice method in view called    

1293
01:06:06,563 --> 01:06:10,865
willRemoveSubview.              
And of course,                  

1294
01:06:10,933 --> 01:06:14,135
we're gonna call                
super.willRemoveSubview. And    

1295
01:06:14,204 --> 01:06:17,338
this gets called anytime        
a view gets removed from me,    

1296
01:06:17,407 --> 01:06:20,774
which is perfect. All I'm       
gonna say here is I'm just      

1297
01:06:20,843 --> 01:06:25,212
gonna check to make sure that   
this view that's being removed  

1298
01:06:25,281 --> 01:06:29,150
is actually in the              
labelObservation tier. So I'm   

1299
01:06:29,219 --> 01:06:35,990
gonna say if LabelObservations  
subview does not equal nil,     

1300
01:06:36,058 --> 01:06:41,062
in other words it will have     
an observation for it.          

1301
01:06:41,131 --> 01:06:43,998
Then I'm gonna set              
the labelObservation for        

1302
01:06:44,067 --> 01:06:47,635
that subview to nil.            
Boom, it just left the heap.    

1303
01:06:47,703 --> 01:06:51,105
As soon as I clear that thing   
out of this it went away.       

1304
01:06:51,174 --> 01:06:53,508
It stops observing which        
is exactly what I want,         

1305
01:06:53,577 --> 01:06:54,776
everyone got that?              

1306
01:06:54,845 --> 01:06:56,877
So that's all we need           
to do to do this.               

1307
01:06:56,946 --> 01:07:02,483
Let's make sure we didn't       
break anything here. Okay so    

1308
01:07:02,552 --> 01:07:05,319
we got our Apple Bees right     
here. Let's change something.   

1309
01:07:05,388 --> 01:07:07,855
Okay let's take this eight      
ball and move it over here.     

1310
01:07:07,924 --> 01:07:10,091
And then let's try and          
threaten,                       

1311
01:07:10,160 --> 01:07:14,061
oops let's get our console      
up here. [INAUDIBLE] here,      

1312
01:07:14,130 --> 01:07:19,233
okay let's threaten             
to go somewhere else.           

1313
01:07:19,302 --> 01:07:24,505
Woo-hoo, it auto saved!         
It worked again. All right,     

1314
01:07:24,574 --> 01:07:29,477
sound good?                     
Back to our slides.             

1315
01:07:29,545 --> 01:07:34,482
Good timing here.               
Now you remember                

1316
01:07:34,551 --> 01:07:37,185
we talked about the view        
controller lifecycle right?     

1317
01:07:37,254 --> 01:07:39,453
View will appear, view did      
appear, all these things.       

1318
01:07:39,522 --> 01:07:42,323
Well the same kind of thing     
happens with your application   

1319
01:07:42,392 --> 01:07:44,425
and it kind of goes through     
this chart up here.             

1320
01:07:44,494 --> 01:07:47,061
So, I'm going to talk about     
how it transitions through      

1321
01:07:47,129 --> 01:07:48,296
all these stages, but           

1322
01:07:48,365 --> 01:07:51,065
first I'm going to talk about   
the stages. So first of all     

1323
01:07:51,134 --> 01:07:55,569
there is Foreground Inactive    
and that is where your code is  

1324
01:07:55,638 --> 01:07:59,073
running, but you're not         
getting any UI events. So you   

1325
01:07:59,142 --> 01:08:01,943
can't do anything. So you can   
only do kind of preparation     

1326
01:08:02,011 --> 01:08:05,880
work in this space. Then        
there's Foreground Active.      

1327
01:08:05,949 --> 01:08:07,848
This is the normal              
state you're used to.           

1328
01:08:07,917 --> 01:08:10,484
Getting UI events, view         
controllers coming on screen,   

1329
01:08:10,553 --> 01:08:11,886
segueing, you're                
doing all your stuff.           

1330
01:08:11,954 --> 01:08:14,288
This is the normal running      
state of your app.              

1331
01:08:14,357 --> 01:08:18,292
Then there's Background.        
In the background your code is  

1332
01:08:18,361 --> 01:08:21,061
running, you are not            
getting any UI events,          

1333
01:08:21,130 --> 01:08:22,863
you never live here for long,   

1334
01:08:22,932 --> 01:08:27,035
maybe 30 seconds. So this is    
transitory state, so anything   

1335
01:08:27,103 --> 01:08:30,338
you do in the background state  
you gotta do it fast. And       

1336
01:08:30,406 --> 01:08:33,974
then you go into this state     
Suspended. Here your code is    

1337
01:08:34,043 --> 01:08:36,911
not running. It's important     
to understand no code in your   

1338
01:08:36,980 --> 01:08:41,516
app anywhere runs. Your app is  
not getting any CPU cycles.     

1339
01:08:41,584 --> 01:08:43,685
Now what's important            
about this state is that        

1340
01:08:43,753 --> 01:08:49,323
you could be killed at anytime  
in this state. All right,       

1341
01:08:49,392 --> 01:08:52,060
so let's talk about how         
we transition here. One         

1342
01:08:52,128 --> 01:08:55,029
transition is launching your    
app. So when you launch your    

1343
01:08:55,098 --> 01:08:57,665
app, you go from not running    
where your binary is not even   

1344
01:08:57,734 --> 01:09:01,602
executing, to briefly,          
the foreground inactive state,  

1345
01:09:01,670 --> 01:09:04,171
and the foreground active       
state. So you do pass through   

1346
01:09:04,240 --> 01:09:06,741
that foreground inactive state  
briefly on your way to running  

1347
01:09:06,809 --> 01:09:09,410
when you launch. Now, another   
important one is when you       

1348
01:09:09,479 --> 01:09:11,279
switch to another application,  
right?                          

1349
01:09:11,347 --> 01:09:13,380
So you're the active app,       
someone's using you, and        

1350
01:09:13,449 --> 01:09:15,616
then they switch                
to another app.                 

1351
01:09:15,685 --> 01:09:19,287
And when that happens, you go   
up to Foreground Inactive for   

1352
01:09:19,355 --> 01:09:22,857
just a moment, and then all     
the way down to Background,     

1353
01:09:22,926 --> 01:09:25,960
you sit in the Background for   
maybe 30 seconds, and           

1354
01:09:26,029 --> 01:09:28,329
then you move to Suspended.     
And                             

1355
01:09:28,398 --> 01:09:30,698
now from Suspended either       
you get reactivated,            

1356
01:09:30,767 --> 01:09:35,870
if they come back to you, or    
you get killed at some point.   

1357
01:09:35,938 --> 01:09:38,539
Those are transitories.         
When you get killed,            

1358
01:09:38,608 --> 01:09:41,275
you go directly from            
Suspended to Not running.       

1359
01:09:41,344 --> 01:09:43,811
You don't pass through some     
state where you get to run any  

1360
01:09:43,879 --> 01:09:47,515
code. Let's talk about          

1361
01:09:47,583 --> 01:09:50,952
how you get notified for        
all of these transitions.       

1362
01:09:51,020 --> 01:09:54,388
What happens and what           
you're supposed to do. Now,     

1363
01:09:54,457 --> 01:09:55,590
all of these things             
I'm going to tell you,          

1364
01:09:55,658 --> 01:09:59,160
by the way, not really that     
important. Because a lot of     

1365
01:09:59,229 --> 01:10:02,930
things are taken care of for    
you. For example, UIDocument,   

1366
01:10:02,999 --> 01:10:05,466
you notice how when we          
threaten to go to another app,  

1367
01:10:05,535 --> 01:10:09,303
it autosaved. It knows about    
these transitions. It's doing   

1368
01:10:09,372 --> 01:10:10,905
that for you, so you don't      
even need to do anything.       

1369
01:10:10,973 --> 01:10:13,273
And that's true of a lot        
of things in iOS. So            

1370
01:10:13,342 --> 01:10:14,876
I'm gonna show you              
all of these things.            

1371
01:10:14,944 --> 01:10:16,277
And the way you do it,          
but most of the time,           

1372
01:10:16,346 --> 01:10:18,646
you don't even need to do       
anything. You just need to      

1373
01:10:18,715 --> 01:10:20,581
know that these                 
transitions are happening.      

1374
01:10:20,650 --> 01:10:23,217
All right, so the first         
transition is from Not running  

1375
01:10:23,286 --> 01:10:26,287
into this Inactive state,       
this Foreground Inactive.       

1376
01:10:26,355 --> 01:10:29,791
This is kinda like preparing    
your app. When this happens,    

1377
01:10:29,859 --> 01:10:31,592
like all the things that        
happen here that I'm gonna      

1378
01:10:31,660 --> 01:10:34,996
talk about, a method in your    
AppDelegate.swift, you know     

1379
01:10:35,064 --> 01:10:38,365
that stepchild that we keep     
foisting off into supporting    

1380
01:10:38,434 --> 01:10:42,270
files. Actually we did look at  
it last time. Remember it had   

1381
01:10:42,338 --> 01:10:46,507
the thing where you're          
opening the URL? Remember we    

1382
01:10:46,576 --> 01:10:48,943
had that little code in there   
that we were talking about,     

1383
01:10:49,012 --> 01:10:51,512
that UI document browser view   
controller, handles opening     

1384
01:10:51,581 --> 01:10:54,015
the URL for us? So              
we have looked in there. But    

1385
01:10:54,083 --> 01:10:55,182
there's a lot of                
methods in there.               

1386
01:10:55,251 --> 01:10:58,619
And that's what all of these    
transitions have is they call   

1387
01:10:58,687 --> 01:11:00,554
methods in there. And you'll    
see there's stubs in there.     

1388
01:11:00,623 --> 01:11:04,192
If you go look at it there's    
stubs in there, that have       

1389
01:11:04,260 --> 01:11:06,126
commented out stuff that        
kinda tell you about them.      

1390
01:11:06,195 --> 01:11:08,696
So this is all pretty           
well documented in there.       

1391
01:11:08,765 --> 01:11:11,299
By the way,                     
all of these transitions also   

1392
01:11:11,367 --> 01:11:14,101
are broadcast on                
radio stations. So              

1393
01:11:14,170 --> 01:11:16,103
you can just sign up and        
put a closure and               

1394
01:11:16,172 --> 01:11:17,471
want this transition            
to happen,                      

1395
01:11:17,540 --> 01:11:20,641
a closure could be executed,    
all right? So that's important  

1396
01:11:20,710 --> 01:11:23,244
to know as well. Not so useful  
for the very first one which    

1397
01:11:23,312 --> 01:11:25,979
is application will finish      
launching with options.         

1398
01:11:26,048 --> 01:11:28,683
And application did finish      
launching with application,     

1399
01:11:28,751 --> 01:11:31,251
cuz that's one of the first     
time you actually write your    

1400
01:11:31,320 --> 01:11:36,224
own code. And notice that that  
thing has a little dictionary   

1401
01:11:36,292 --> 01:11:39,260
passed in, right? Application   
will and did finish             

1402
01:11:39,328 --> 01:11:41,962
launching with options.         
That dictionary tells you       

1403
01:11:42,031 --> 01:11:45,566
why you were launched. Now,     
why would you be launched?      

1404
01:11:45,634 --> 01:11:47,901
Well, of course the user might  
have touched on your icon.      

1405
01:11:47,970 --> 01:11:50,604
That's most of the time.        
But you can also get launched   

1406
01:11:50,673 --> 01:11:52,806
because someone wants           
you to open a document.         

1407
01:11:52,875 --> 01:11:53,941
We're EmojiArt, and             

1408
01:11:54,010 --> 01:11:55,743
someone wants us to open        
an EmojiArt document and        

1409
01:11:55,811 --> 01:11:58,746
we're not running, we could     
get launched to do that. You    

1410
01:11:58,815 --> 01:12:02,483
can also set up things where    
you get launched when the user  

1411
01:12:02,551 --> 01:12:05,986
walks by a dry cleaner.         
You can actually register       

1412
01:12:06,055 --> 01:12:10,691
a Place in the world and walk   
by, boom, you'll get launched.  

1413
01:12:10,759 --> 01:12:13,894
You can also have this          
activity continuation thing,    

1414
01:12:13,963 --> 01:12:16,631
where you're working in         
emoji art on your iPad,         

1415
01:12:16,700 --> 01:12:18,932
and then you switch             
over to your iPhone.            

1416
01:12:19,001 --> 01:12:20,802
And then in the corner there's  
a little icon you press.        

1417
01:12:20,870 --> 01:12:22,303
Now you're right back in        
emoji art where you were.       

1418
01:12:22,371 --> 01:12:25,973
Well that might have to         
launch you. You might get       

1419
01:12:26,042 --> 01:12:29,543
a push notification. You're     
using Cloud Kit, something in   

1420
01:12:29,612 --> 01:12:32,179
your database changed, you get  
woken up to say, hey, look,     

1421
01:12:32,248 --> 01:12:34,615
you got a push                  
notification for you. So        

1422
01:12:34,683 --> 01:12:37,685
there's a lot of reasons you    
get woken up, and launched,     

1423
01:12:37,754 --> 01:12:40,520
and that dictionary will        
contain all the information     

1424
01:12:40,589 --> 01:12:44,525
you need to know about why. It  
used to be that an application  

1425
01:12:44,594 --> 01:12:47,695
will and did finish launching.  
We built our UI.                

1426
01:12:47,764 --> 01:12:50,831
We created a split view. We     
created a navigation control.   

1427
01:12:50,900 --> 01:12:53,534
We put a view controller.       
We never do that anymore.       

1428
01:12:53,603 --> 01:12:55,569
I only mention this because,    
your final project,             

1429
01:12:55,638 --> 01:12:58,038
you're gonna go out and Google  
things and look Internet. And   

1430
01:12:58,107 --> 01:13:01,108
you're gonna see people say,    
go create a split view in your  

1431
01:13:01,177 --> 01:13:03,911
ApplicationDidFinishLaunching   
with options. No,               

1432
01:13:03,979 --> 01:13:06,347
we don't do that. Storyboards,  
that's how we do it.            

1433
01:13:06,416 --> 01:13:09,250
Those answers were              
pre storyboard. Or              

1434
01:13:09,318 --> 01:13:13,054
someone who never got the       
storyboard story. We build our  

1435
01:13:13,122 --> 01:13:16,790
UI in storyboards, not in       
these method, in this method.   

1436
01:13:16,859 --> 01:13:20,761
All right, the next transition  
is actually coming to           

1437
01:13:20,830 --> 01:13:22,830
that inactive state             
from the other side.            

1438
01:13:22,899 --> 01:13:24,398
You were the active app, and    

1439
01:13:24,467 --> 01:13:26,200
not you're not gonna            
be the active app.              

1440
01:13:26,268 --> 01:13:28,202
Probably because the user       
clicked on another app.         

1441
01:13:28,271 --> 01:13:30,737
This one is                     
ApplicationWillResignActive,    

1442
01:13:30,806 --> 01:13:32,873
because that's                  
what's happening.               

1443
01:13:32,942 --> 01:13:36,744
Here you wanna think of         
this as a the pause button.     

1444
01:13:36,812 --> 01:13:39,346
You wanna pause whatever is     
happening in your app right     

1445
01:13:39,415 --> 01:13:42,349
here. So let's say I use the    
example of an Asteroids game.   

1446
01:13:42,418 --> 01:13:45,419
Your shooting Asteroids. You    
want the whole Asteroid field   

1447
01:13:45,487 --> 01:13:50,291
to pause when you get this.     
And then the next one           

1448
01:13:50,359 --> 01:13:54,829
here is a inactive to active,   
that, unpause.                  

1449
01:13:56,699 --> 01:13:58,865
So this is                      
ApplicationDidBecomeActive. So  

1450
01:13:58,934 --> 01:14:02,069
you kinda wanna have a pause,   
unpause thing here. Now,        

1451
01:14:02,138 --> 01:14:04,338
with a lot of apps, it doesn't  
make sense. You never pause or  

1452
01:14:04,407 --> 01:14:07,341
unpause. They're not that       
kinda app. They, they just      

1453
01:14:07,410 --> 01:14:08,876
are what they are, so           
you don't have to do anything.  

1454
01:14:08,945 --> 01:14:11,779
But if you have an app where    
things would make sense         

1455
01:14:11,848 --> 01:14:14,515
to pause, this is where you     
pause and unpause in these two  

1456
01:14:14,584 --> 01:14:19,486
things. Now, this one,          
right here, is, someone         

1457
01:14:19,555 --> 01:14:22,323
clicked on another app, you've  
gone through active, inactive,  

1458
01:14:22,391 --> 01:14:24,558
now you're going around         
to this background state.       

1459
01:14:24,627 --> 01:14:26,593
This is                         
ApplicationDidEnterBackground.  

1460
01:14:26,662 --> 01:14:30,330
It's time right here to         
batten down the hatches.        

1461
01:14:30,399 --> 01:14:33,934
Close your files, get yourself  
in a situation where you could  

1462
01:14:34,003 --> 01:14:36,637
be killed. You've got about 30  
seconds here to prepare to be   

1463
01:14:36,706 --> 01:14:38,538
killed.                         
You might not be killed,        

1464
01:14:38,607 --> 01:14:42,143
but you might be. So you wanna  
not have any files open,        

1465
01:14:42,211 --> 01:14:44,411
that are gonna get corrupted    
if they get closed, or          

1466
01:14:44,480 --> 01:14:49,049
an unsaved data in your app,    
close things up here. and       

1467
01:14:49,118 --> 01:14:51,752
you get 30 seconds to do it.    
You can ask for an extension,   

1468
01:14:51,820 --> 01:14:54,054
short extensions of time,       
but if you ask too much,        

1469
01:14:54,123 --> 01:14:56,457
the system will stop granting   
you those exceptions,           

1470
01:14:56,526 --> 01:14:57,324
extensions.                     

1471
01:14:57,392 --> 01:15:00,027
So pretty much think about,     
you've got 30 seconds or so     

1472
01:15:00,096 --> 01:15:06,099
to get your hatches battened    
here. The next one here is      

1473
01:15:06,168 --> 01:15:07,801
applicationwillEnterForegro-    
und.                            

1474
01:15:07,870 --> 01:15:09,737
So here, you went down          
the background view,            

1475
01:15:09,806 --> 01:15:12,740
you battened down the hatches,  
and you got activated again.    

1476
01:15:12,809 --> 01:15:15,576
You didn't get killed.          
Here you wanna un-batten down   

1477
01:15:15,645 --> 01:15:19,013
the hatches. Open back up the   
things that you had closed.     

1478
01:15:19,081 --> 01:15:20,681
Now, a lot of times you don't   
need to do anything here,       

1479
01:15:20,750 --> 01:15:23,517
because you're opening up       
things that you closed          

1480
01:15:23,586 --> 01:15:26,153
in the battening down           
the hatches, on demand anyway.  

1481
01:15:26,221 --> 01:15:27,622
If you tried to                 
access a file and               

1482
01:15:27,690 --> 01:15:30,057
it's not open, well,            
you'll just open it then. So,   

1483
01:15:30,125 --> 01:15:31,792
oftentimes you don't have       
to do anything here, and        

1484
01:15:31,861 --> 01:15:35,162
I kinda recommend writing your  
code in that way. So that you   

1485
01:15:35,230 --> 01:15:39,400
don't really ever have to       
un-batten down the hatches. So  

1486
01:15:39,468 --> 01:15:41,235
that's, all the things          
that happen.                    

1487
01:15:41,303 --> 01:15:43,904
And of all those things you     
get radio station, all those    

1488
01:15:43,973 --> 01:15:47,274
things that have methods in     
the app delegates you can do.   

1489
01:15:47,343 --> 01:15:50,144
But the AppDelegate does some   
other things as well in there.  

1490
01:15:50,213 --> 01:15:53,748
For example, the opening        
URL thing we saw last time,     

1491
01:15:53,816 --> 01:15:56,517
it also can do                  
background fetching.            

1492
01:15:56,585 --> 01:15:57,417
Which is kind of cool.          

1493
01:15:57,486 --> 01:15:58,886
Let's say you have              
a Twitter client, or            

1494
01:15:58,954 --> 01:16:01,789
something like that, and when   
someone launches your app,      

1495
01:16:01,857 --> 01:16:03,791
you wanna show them             
the latest Tweets. Well,        

1496
01:16:03,860 --> 01:16:07,061
you can actually say to your    
app to fetch the latest Tweets  

1497
01:16:07,129 --> 01:16:09,429
in the background, even when    
your app is not running. And    

1498
01:16:09,498 --> 01:16:11,999
what'll happen is, it'll get    
launched, but it won't come on  

1499
01:16:12,067 --> 01:16:14,101
screen, and you'll be in        
that background state for       

1500
01:16:14,170 --> 01:16:15,335
a little, little bit of time,   

1501
01:16:15,404 --> 01:16:17,805
where you're allowed to make a  
couple of network requests for  

1502
01:16:17,874 --> 01:16:20,808
your 30 seconds or whatever.    
And then you go back to sleep.  

1503
01:16:20,877 --> 01:16:23,477
So, you can do that with        
AppDelegate. It also manages    

1504
01:16:23,545 --> 01:16:26,280
data protection. I don't        
know if you know this but,      

1505
01:16:26,349 --> 01:16:29,382
when your device is locked in   
the lock screen, apps cannot    

1506
01:16:29,451 --> 01:16:33,020
see the data. It's encrypted.   
It is fully encrypted, so you,  

1507
01:16:33,089 --> 01:16:35,422
the apps couldn't do            
anything if they wanted to.     

1508
01:16:35,490 --> 01:16:38,525
So, the AppDelegate will tell   
you what's going on about       

1509
01:16:38,594 --> 01:16:42,496
when you can access the files,  
things like that. There's also  

1510
01:16:42,565 --> 01:16:46,100
a UIApplication, which the      
AppDelegate is delegate of.     

1511
01:16:46,168 --> 01:16:48,035
We never subclassed             
UIApplication,                  

1512
01:16:48,103 --> 01:16:51,338
we use the AppDelegate to       
configure it's functionality.   

1513
01:16:51,407 --> 01:16:53,774
However, UIApplication does     
have a few interesting things.  

1514
01:16:53,843 --> 01:16:58,479
Like, it has a method so you    
can open a URL in another app.  

1515
01:16:58,548 --> 01:17:01,948
So, your image gallery, and     
maybe you asked to open         

1516
01:17:02,017 --> 01:17:05,119
an emoji art document. You      
can ask using that open URL.    

1517
01:17:05,187 --> 01:17:07,621
Here's where you register for   
push notifications.             

1518
01:17:07,690 --> 01:17:09,489
So, this is something you       
have to do if you want that     

1519
01:17:09,558 --> 01:17:11,625
Cloud Kit thing to notify you.  
You have to register for        

1520
01:17:11,694 --> 01:17:14,595
push notifications there. You   
can set the fetch interval for  

1521
01:17:14,664 --> 01:17:16,630
that background fetching        
I talked about.                 

1522
01:17:16,699 --> 01:17:18,899
Here's where you ask for        
more time, if you're in         

1523
01:17:18,968 --> 01:17:20,968
the background mode, and        
you need a little bit           

1524
01:17:21,037 --> 01:17:24,271
more time to finish up. That's  
happening in UI application.    

1525
01:17:24,340 --> 01:17:27,974
The little spinner in the top   
left of your device that says   

1526
01:17:28,043 --> 01:17:31,812
there's network activity,       
that's controlled with this     

1527
01:17:31,881 --> 01:17:33,947
bool.                           
Unfortunately it's a bool.      

1528
01:17:34,016 --> 01:17:36,417
So if you have multiple         
threads acting as a network,    

1529
01:17:36,485 --> 01:17:38,886
they gotta share this bool,     
it's kind of annoying,          

1530
01:17:38,954 --> 01:17:41,521
but. And you can also           
find out about things,          

1531
01:17:41,590 --> 01:17:44,291
like how much time do I have    
left to run in the background?  

1532
01:17:44,360 --> 01:17:46,994
What is that preferred content  
size category, you know,        

1533
01:17:47,062 --> 01:17:49,496
the slider for the font size?   
What state am I in?             

1534
01:17:49,565 --> 01:17:50,564
Am I in the foreground,         

1535
01:17:50,633 --> 01:17:51,899
the background, where am I?     

1536
01:17:51,968 --> 01:17:55,602
You can find all those things   
out with UIApplication. All     

1537
01:17:55,671 --> 01:17:58,606
right, quickly Info.plist, we   
already saw Info.plist in your  

1538
01:17:58,674 --> 01:18:01,976
homework. You used it to add    
that app transport security,    

1539
01:18:02,044 --> 01:18:06,446
right? You can actually         
edit this directly in XML,      

1540
01:18:06,515 --> 01:18:09,150
you just right click on it and  
switch to sources XML,          

1541
01:18:09,218 --> 01:18:12,485
you can do that.                

1542
01:18:12,554 --> 01:18:15,122
will get a snippet of XML from  
somebody that does something,   

1543
01:18:15,190 --> 01:18:17,624
enables something in plist,     
and you're gonna paste it in    

1544
01:18:17,693 --> 01:18:20,727
here. But usually we don't      
even edit the plist thing       

1545
01:18:20,796 --> 01:18:23,630
directly like we do with        
App Transport Security.         

1546
01:18:23,699 --> 01:18:25,399
We edit it in                   
the project settings,           

1547
01:18:25,468 --> 01:18:27,634
like we did with                
the document types, right?      

1548
01:18:27,703 --> 01:18:29,936
The document types we had for   
Emoji Art View, and for         

1549
01:18:30,005 --> 01:18:33,941
your image gallery. We edited   
that all in project settings.   

1550
01:18:34,010 --> 01:18:37,912
And the project settings is     
mostly editing the Info.plist   

1551
01:18:37,980 --> 01:18:40,881
indirectly. And finally,        
we have the capabilities.       

1552
01:18:40,950 --> 01:18:42,516
We talked about this            
with Cloud Kit.                 

1553
01:18:42,585 --> 01:18:45,219
There are certain things,       
that to use them you            

1554
01:18:45,288 --> 01:18:48,889
have to turn them on. This      
capabilities tab inside of      

1555
01:18:48,958 --> 01:18:51,725
your project                    
settings like this.             

1556
01:18:51,794 --> 01:18:55,462
Some of these things require    
servers, like Apple Pay,        

1557
01:18:55,531 --> 01:18:59,934
and iCloud, and Game Center.    
Some don't, like Maps, and      

1558
01:19:00,002 --> 01:19:04,071
Inner App Audio, Home Kit,      
none of those do.               

1559
01:19:04,140 --> 01:19:07,074
The things that require         
a server, you can only turn     

1560
01:19:07,143 --> 01:19:10,544
these on if you are a member    
of an Apple developer program.  

1561
01:19:10,612 --> 01:19:13,613
That costs $99 a year. And      
you can kinda see why that is,  

1562
01:19:13,682 --> 01:19:16,383
because to access these server  
technologies, they're kinda     

1563
01:19:16,452 --> 01:19:18,718
needs to be stuff in that       
server that knows about you,    

1564
01:19:18,787 --> 01:19:20,387
and this providing stuff.       
Well,                           

1565
01:19:20,456 --> 01:19:23,723
somebody's got, they gotta      
know who you are for real.      

1566
01:19:23,792 --> 01:19:26,193
You can't just be some          
random Apple ID out there.      

1567
01:19:26,262 --> 01:19:27,794
You wanna be registered         
in the program.                 

1568
01:19:27,863 --> 01:19:31,999
And the $99 seems to me to be   
mostly an administrative fee.   

1569
01:19:32,068 --> 01:19:34,769
That's not very much money for  
the amount of functionality     

1570
01:19:34,837 --> 01:19:36,570
that you're getting             
with all these servers,         

1571
01:19:36,639 --> 01:19:39,139
push notifications, all these   
things. It's all covered in     

1572
01:19:39,208 --> 01:19:43,476
one $99 per year fee. I don't   
have time to cover all these,   

1573
01:19:43,545 --> 01:19:45,612
but this is a great place       
to go look for interesting,     

1574
01:19:45,681 --> 01:19:48,749
not covered in lecture things   
to do. Go look through this     

1575
01:19:48,818 --> 01:19:51,018
list and see if you can find    
something fun to do in there.   

1576
01:19:51,087 --> 01:19:54,288
All right, that is it.          
On Wednesday,                   

1577
01:19:54,356 --> 01:19:57,191
we're gonna talk about super    
important topic, and I, this    

1578
01:19:57,259 --> 01:19:59,960
is the last topic I cover,      
really, before you launch into  

1579
01:20:00,029 --> 01:20:02,730
your final projects this week,  
which is segues.                

1580
01:20:02,798 --> 01:20:05,833
We know about show segues, and  
show detail segues, right?      

1581
01:20:05,901 --> 01:20:08,068
The navigation controller and   
the split view controller.      

1582
01:20:08,136 --> 01:20:09,937
And we know about modal         
segues too, a little bit.       

1583
01:20:10,005 --> 01:20:12,439
We put put up our emoji         
art document modally. But       

1584
01:20:12,508 --> 01:20:15,342
we're gonna learn pop over      
segue's, more than just for     

1585
01:20:15,411 --> 01:20:17,877
alerts, but pop over            
segue's in general. Also,       

1586
01:20:17,946 --> 01:20:20,714
unwinding segue's, and embed    
segue's, two kind of under      

1587
01:20:20,783 --> 01:20:23,517
appreciated segue's that you    
can do that are kind of cool.   

1588
01:20:23,585 --> 01:20:26,053
We're gonna learn all about     
that, and I'll be demoing it    

1589
01:20:26,122 --> 01:20:29,356
all on Wednesday as well.       
Next week is Thanksgiving.      

1590
01:20:29,425 --> 01:20:32,292
So, you get a week off.         
That will be great, and         

1591
01:20:32,361 --> 01:20:35,462
then we'll back at it           
the week after. All right,      

1592
01:20:35,530 --> 01:20:38,198
see you on Wednesday.           
>> For                          

1593
01:20:38,267 --> 01:20:47,674
more, please visit              
us at stanford.edu.             
