Kivy : Error weakly-referenced object (in a clock function) no longer exists

问题

So here is my error code I think there's something hard in this error, i looked on forums but couldn't find out.

And ... i have the error on my phone (with kivy launcher python 3 and when i build with buildozer) but not on my computer (ubuntu 18.0.4 and windows 10) The error, from what i understand, comes from the garbage collector that delete a reference and the code try to access the reference after the garbage collector. but i am not sure if I rly understand the garbage collector thing

What i tried :

make "strong references" so the gc dont delete it with:

    id: id.__self__

in my kv file

make "strong references" with :

     self.refs = [
                self.id.__self__,
                self.id.__self__]

-Use the ErrorHandler to handle the error but the error keep coming for ever

What I think cause the error but I have no idea how to fix it:

the clock I use to send request to the server but i don't know why (self.requestClient is a function to send a request) :

C = Clock.schedule_interval(self.requestClient, 5)
this information in the kivy clock documentation :

Important

The callback is weak-referenced: you are responsible for keeping a reference to your original object/callback. If you don’t keep a reference, the ClockBase will never execute your callback

Error :

[ERROR  ] Exception catched by ExceptionHandler
05-07 11:27:45.694  2788  2823 I python  : Traceback (most recent call last):
05-07 11:27:45.694  2788  2823 I python  :   File path/kivy-launcher/.buildozer/android/platform/build-armeabi-v7a/build/python-installs/launcher/kivy/core/window/window_sdl2.py", line 747, in mainloop
05-07 11:27:45.694  2788  2823 I python  :   File "/path/kivy-launcher/.buildozer/android/platform/build-armeabi-v7a/build/python-installs/launcher/kivy/core/window/window_sdl2.py", line 479, in _mainloop
05-07 11:27:45.694  2788  2823 I python  :   File "/path/kivy-launcher/.buildozer/android/platform/build-armeabi-v7a/build/python-installs/launcher/kivy/base.py", line 339, in idle
05-07 11:27:45.694  2788  2823 I python  :   File "/path/kivy-launcher/.buildozer/android/platform/build-armeabi-v7a/build/python-installs/launcher/kivy/clock.py", line 591, in tick
05-07 11:27:45.694  2788  2823 I python  :   File "kivy/_clock.pyx", line 384, in kivy._clock.CyClockBase._process_events
05-07 11:27:45.694  2788  2823 I python  :   File "kivy/_clock.pyx", line 414, in kivy._clock.CyClockBase._process_events
05-07 11:27:45.694  2788  2823 I python  :   File "kivy/_clock.pyx", line 412, in kivy._clock.CyClockBase._process_events
05-07 11:27:45.694  2788  2823 I python  :   File "kivy/_clock.pyx", line 154, in kivy._clock.ClockEvent.tick
05-07 11:27:45.694  2788  2823 I python  :   File "kivy/_clock.pyx", line 86, in kivy._clock.ClockEvent.get_callback
05-07 11:27:45.694  2788  2823 I python  :   File "/path/kivy-launcher/.buildozer/android/platform/build-armeabi-v7a/build/python-installs/launcher/kivy/weakmethod.py", line 56, in is_dead
05-07 11:27:45.694  2788  2823 I python  : ReferenceError: weakly-referenced object no longer exists

Thanks for reading !

回答1:

The official documentation (Kv language Programming Guide) says to add 'strong' references such as id_name: id_name.__self__ in the KV code, but it is unclear where this is necessary. What's more, it did not solve the ReferenceError: weakly-referenced object no longer exists errors for me.

What did work is forcing Buildozer to use a specific version of hostpython3 by adding this to the requirements line of the buildozer.spec file:

python3==3.7.5, hostpython3==3.7.5

One more note: after adding the above to requirements, I went back and removed all my __self__ references and it still worked fine, so apparently these are no longer needed in Kivy KV language.

Credit for this goes to the beautiful answer from leo10011.

Update 2020-05-19: This bug reportedly has been fixed in Kivy 2.0.