Using UIAlertController

You can choose whether to display as an alert or action sheet style.

Using Alert style

The alert style presents modally in the center of their presenting view controllers.

Step 1: Create the UIAlertController

Create the alert controller as below, setting preferredStyle to Alert

let alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)

UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Title"
                                                                           message:@"Message"
                                                                    preferredStyle:(UIAlertControllerStyleAlert)];

Step 2: Add buttons

Create a UIAlertAction for each button to display and respond to.

// create a cancel action
let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) { (action) in
    // handle cancel response here. Doing nothing will dismiss the view.
}
// add the cancel action to the alertController
alertController.addAction(cancelAction)

// create an OK action
let OKAction = UIAlertAction(title: "OK", style: .default) { (action) in
    // handle response here.
}
// add the OK action to the alert controller
alertController.addAction(OKAction)

// create a cancel action
UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"Cancel"
                                                    style:UIAlertActionStyleCancel
                                                  handler:^(UIAlertAction * _Nonnull action) {
                                                         // handle cancel response here. Doing nothing will dismiss the view.
                                                  }];
// add the cancel action to the alertController
[alert addAction:cancelAction];

// create an OK action
UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"OK"
                                                   style:UIAlertActionStyleDefault
                                                 handler:^(UIAlertAction * _Nonnull action) {
                                                         // handle response here.
                                                 }];
// add the OK action to the alert controller
[alert addAction:okAction];

Adding two buttons will place them side by side in the alert. Adding more than two buttons stacks them in the view similar to the ActionSheet style.

Step 3: Show the UIAlertController

present(alertController, animated: true) {
    // optional code for what happens after the alert controller has finished presenting
}

[self presentViewController:alert animated:YES completion:^{
    // optional code for what happens after the alert controller has finished presenting
}];

If you wish to call present() outside a view controller, you would do:

UIApplication.shared.keyWindow?.rootViewController?.present(alertController, animated: true) {
    // optional code for what happens after the alert controller has finished presenting
}

[[UIApplication sharedApplication].keyWindow.rootViewController presentViewController:alert
                                                                             animated:YES
                                                                           completion:^{
                                                                                   // optional code for what happens after the alert controller has finished presenting
                                                                           }];

Using Action Sheets style

The action sheet style anchors the view to the bottom of the presenting view controller.

Step 1: Create the UIAlertController

Create the alert controller as below, setting preferredStyle to ActionSheet

let alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .actionSheet)

Step 2: Add buttons

Create a UIAlertAction for each button to display and respond to. The destructive style options shows the button text in red.

let logoutAction = UIAlertAction(title: "Log Out", style: .destructive) { (action) in
    // handle case of user logging out
}
// add the logout action to the alert controller
alertController.addAction(logoutAction)     

let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) { (action) in
    // handle case of user canceling. Doing nothing will dismiss the view.
}
// add the cancel action to the alert controller
alertController.addAction(cancelAction)

Step 3: Show the UIAlertController

present(alertController, animated: true) {
    // optional code for what happens after the alert controller has finished presenting
}