Markor (inconsistent GUI states - Undo and Redo behave inconsistently when doing text editing)

[functional-fuzzing-android-apps]

The bug was found in the latest release (version 2.0.1). The bug can be reproduced on an Android emulator 6.0 and a Google Pixel 3 XL phone.

Description

The undo and redo behave inconsistenly when doing text editing. See the video below.

https://youtu.be/1mO0RbX5g_4

Let me explain the video content and the issue in detail.

Step 1: I input a line of text, which contains a priority (C) and a letter Y. Now, if I toggle between undo and redo, the text can switch between (C) Y and (C). It is correct and expected functionality.

Step 2: I keep the text as (C) Y. Then, I switch to Tab QuickNote and come back. At this time, I can toggle between undo and redo (as they are enabled on the GUI page), but the text will not change, and remain same as (C) Y. Okay, I guess the switch action internally writes the text into disk, so the user cannot use the undo and redo function. Let's assume this is correct and intended functionality. Although, I feel this is quite strange and does not conform to my intution.

Step 3: Then, I delete Y. Now, I find if I toggle between undo and redo again, the text can switch between (C) and (C) Y. It is correct and expected functionality.

Step 4: I keep the text as (C). Then, I switch to Tab QuickNote and come back. Note I can still toggle between undo and redo (as they are enabled on the GUI page), but the text will not change, and remain same as (C) .

Step 5: Then, I delete (C) . Now, I find if I toggle between undo and redo again, the text can switch between (C) and empty. It is correct and expected functionality.

Step 6: I keep the text as empty. Then, I switch to Tab QuickNote and come back. Note I can toggle between undo and redo (as they are enabled on the GUI page), but at this time the text CAN be changed. The text can switch between (C) and empty. This behavior is obviously inconsistent with my previous assumption on this functionality.

Now, I become quite confused about the exact logic behind undo and redo. When the text cannot be changed in Step 2 and 4, why the undo and redo button are enabled on the GUI page? --- It gives me the intuition that these two buttons will function to change the text.

So, my suggestion is: (1) disable undo and redo on the GUI page (show them in gray) when the file was written to the disk; or (2) still enable undo and redo to function as expected (i.e., able to change the text) when the file was written.