Weird bug with keyboard bindings on Android

[Jimminer]

I stumbled upon a bug that from what I can tell, bugs out the keyboard binding.

Any suggestions on fixing this would be appreciated!

Setup:

I managed to reproduce this bug with 2 screens.

The first screen has a button (that takes you to the second screen) and a MDTextField

(I'm running Android 12 and built the apk with buildozer)

How to reproduce (see code below):

I could not reproduce on a Desktop machine! Only on Android

1. Open the app and just touch the text field (typing is not necessary)

2. Press the button (named "submit")

3. Try to press the Android's back button

If nothing happened, you reproduced the bug (normally a toast should come up)

Temporary solution:

While being in the bugged state (having at least touched the text field), either go to your

home screen or your recent apps screen (Without closing the app!) and reopen the app

Couldn't reproduce?

This is a video showing the following:

1. A run without touching the text field

2. A run with touching the text field (the bug) and doing the temporary solution

Code:

##############################################

from kivy.lang import Builder

from kivy.utils import platform

from kivy.core.window import Window

from kivy.clock import Clock

from kivy.uix.screenmanager import Screen

from kivymd.app import MDApp

if platform == "android":

     from kivymd.toast.androidtoast import toast

else:

     from kivymd.toast import toast

KV = """

MDScreen:

     MDNavigationLayout:

    ScreenManager:

        id: screenManager

        FirstScreen:

            name: "firstScreen"

        MainScreen:

            name: "mainScreen"

<FirstScreen>:

    MDBoxLayout:

        orientation: "vertical"

        MDFlatButton:

            text: "submit"

            on_release: app.submit()

        MDTextField:

            id: testfield

<MainScreen>:

    MDLabel:

        text: "main screen"

"""

class FirstScreen(Screen):

    def on_enter(self):

        pass

class MainScreen(Screen):

    def on_enter(self):

        pass

class MainApp(MDApp):

    def build(self):

        Window.bind(on_keyboard=self.keyboardBindings)

        return Builder.load_string(KV)

    def keyboardBindings(self, window, key, *largs):

        if key == 27:

            toast("ESC was pressed")

            return True

    def submit(self):

        testfield_text = self.root.ids.screenManager.get_screen("firstScreen").ids.testfield.text

        self.root.ids.screenManager.current = "mainScreen"

app = MainApp()

if __name__ == "__main__":

    app.run()

##############################################

The line where the variable testfield_text is set (inside submit function) is mandatory for the bug to happen!

[Robert]

I think the expected behavior is:

1) if a text input has focus the first Esc/'Back button/gesture' de-focuses the text input.

2) When text input does not have focus Esc/Back stops the app.

But I notice in the code above the handler return True, so step 2) won't happen.

[Jimminer]

Yes, that would be the expected behavior on an app without the keyboard bound to a function.

As you can also see from the video I posted, I do not press the back button while the text field is focused. To unfocus the text field I just tap anywhere on the screen (except the keyboard of course)

The expected behavior for this app should be a Toast displaying "ESC was pressed" whenever the back button is pressed. That is the case when running on desktop but not on Android!

After all, this is just reproducible code and it doesn't serve the same purpose as my main code. On my main code I use the back button as a "previous screen" trigger (where I also experience the same problem on Android)

Returning True lets the handler know that my function took care of the event and there's no need for kivy to do anything and ultimately should not be the cause of the problem.

[Robert]

> Returning True lets the handler know that my function took care of the event and there's no need for kivy to do anything and ultimately should not be the cause of the problem.

This is not my understanding of the operation. We'll have to agree to differ.

[Jimminer]

You are correct. I had a bad understanding.

The return just stopped further execution hence why the app was not closing.

The proper way to achieve this without using return is:

from kivy.config import Config

Config.set('kivy', 'exit_on_escape', '0')

Unfortunately, even after this change, the bug still persists.

[Robert]

One down, one to go....

This looks similar https://github.com/kivy/kivy/issues/7374

If you want submit or add to an issue, convert the example to Kivy first.

[Jimminer]

I had seen that issue and some other similar issues and some people said that it's a fault of the sdl2 version that p4a is using.

I tried putting 2.0.10 as the required version of sdl2 (the version which supposedly fixed this bug) in the buildozer.spec but it would throw an error upon building the apk.

I also tried many combinations of android api/kivy versions which all ended up either having the same bug or just not working.

I guess the only solution is to wait for p4a to implement that sdl2 version or create a patch that fixes that specific bug.

[Robert]

p4a a is a huge balancing act, you can change stuff from the current defaults but it almost always breaks something.

[Jimminer]

Yeah, I tried many ways to implement that sdl2 change but as you said, it always broke something.

I will stick with using a button as a previous screen trigger until the bug is fixed.

Thanks for the help!

[Robert]

If you are just using Back to navigate screens, this is a possible alternative:

Create a SwipeScreen that uses a gesture package called CommonGestures  not the Back button/gesture

https://github.com/Android-for-Python/gestures4kivy

https://github.com/Android-for-Python/Common-Gestures-Example#the-examples

[Jimminer]

That's really nice! I will use this from now on. Thank you!