Problem with kivy on Android : Black screen on resume

[Elby]

Hi,

I'm trying to make my first Android application with Kivy.

It's almost working.

I have no problem launching my application on android.

It seems to work fine, except that when Android resume the application, after switching between application or just turn the tablet on/off, I get a black screen.

I can reproduce this behavior with a very simple application:

main.py:

import kivy
kivy.require('1.10.1')

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout

try:
    from android.permissions import request_permissions, Permission
    request_permissions([Permission.READ_EXTERNAL_STORAGE])
    request_permissions([Permission.WRITE_EXTERNAL_STORAGE])
except:
    pass


class ABugLayout(BoxLayout):
    pass


class ABugApp(App):

    def build(self):
        root =  ABugLayout()
        return root

    def on_pause(self, *args, **kwds):
        return True

if __name__ == '__main__':
    app = ABugApp()
    app.run()

abug.kv:

#: kivy 1.10.1

<ABugLayout>:
    orientation: "vertical"
    Label :
        text : "Just a bug"
        size_hint: None, None
        size : self.texture_size

    Image:
        source: "./icons/test.png"

I've build my application on linux with the following configuration:

• Ubuntu 20.04 LTS
• Buildozer 1.2.0
• Python 3.8.1
• Kivy 1.11.1

I have a very simple buildozer.spec file with default configuration.

I've tested this on an android Samsung Galaxy Tab A (Android 9) and on a One Plus 7 phone (Android 10).

Is there anything to configure to prevent that black screen on resume ?

Regards,

Elby

It seems I'm

[Robert Flatt]

Try    on_pause(self)     without the other two arguments.

[Elby]

I've tried that modification but it doesn't change anything.

I've also noted that if I drag down the notification bar, my application become visible again and works normally.

Is there something to setup anywhere to get visible without having to drag the notification bar?

[Robert Flatt]

I have not seen anything like this in a long time, I don't know why it is occuring.

My build environment is the same as yours.

The static calls to request_permissions are unusual, but I don't know why they would break anything.

Do you see the same issue with Hello World?

[K leo]

How about combining on_pause() and on_resume()?  But I would first use some print statements in the two callback functions to see if they are indeed invoked.  From the menu:

Event handler called when your application is resuming from the Pause mode.

Warning

When resuming, the OpenGL Context might have been damaged / freed. This is where you can reconstruct some of your OpenGL state e.g. FBO content.

[Robert Flatt]

How about combining on_pause() and on_resume()?

Not clear to me what the sugestion is.

https://kivy.org/doc/stable/guide/basic.html#kivy-app-life-cycle

When resuming, the OpenGL Context might have been damaged / freed.

Yes that is what it says. But why does nobody else see this?

Can you run Hello World? 

[Robert Flatt]

I tried it, I can replicate using that static call to request_permissions().

This usage is probably ambiguous.

request_permissions() opens a dialog (once per install), so calling before the UI exists has unknown meaning.

Doing that on_resume() doubly so ;)

Call request_permissions() from on_start() .

request_permissions() is asynchronous so if you use that permission immediately the usage should be inside a callback.

Also you need to test if the user says 'Deny'.

Finally check the Android docuumentation, I think you will find WRITE implies READ, so there is only one permission to request needed.

    def on_start(self):
        request_permissions([Permission.WRITE_EXTERNAL_STORAGE])