iOS: App freezes after switching content

I’m trying to create a mobile app with more than just 1 page. For Android, this works fine by replacing the content of the main window: self.app.main_window.content = new_main_box It also works on macOS.

On iOS, the new_main_box is also shown, but then, the UI is completely unresponsive. No button is working, no input field is taking the focus, nothing works anymore and I have to kill the app to get out of this screen. There is no error in the logs, so I have no idea what the problem might be.

I made a minimal demo app to show this problem: https://bitbucket.org/TomArn/demoapp.git branch: iOS_content_switching In this demo app, in addition to the above problem, the new screen is black and I only see the button, but not the label, whereas in the other app where I first found the problem, the screen actually looked pretty OK (except that it was frozen…)

I’m using Python 3.8 on iOS 14.4, Toga 0.3.0dev27

[freakboy3742]

@calvma toga.platform.current_platform contains the currently active platform (as a string; you’re looking for iOS in this case).

[t-arn]

@mshammel Many thanks for your workaround! I can confirm that it is working on iOS 😃 The workaround is now also in the repo, in the branch iOS_content_switching_workaround

I also tested the workaround on Android, but there, I get an error, because Widget.remove() is not implemented there:

2021-02-10 08:00:53.874 5279-5279/com.t_arn.demoapp E/Python: Traceback (most recent call last):
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:   File "/data/user/0/com.t_arn.demoapp/files/python/user_code/app_packages/rubicon/java/api.py", line 44, in dispatch
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:     val = getattr(pyinstance, method)(*args)
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:   File "/data/user/0/com.t_arn.demoapp/files/python/user_code/app_packages/toga_android/widgets/button.py", line 14, in onClick
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:     self.button_impl.interface.on_press(widget=self.button_impl.interface)
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:   File "/data/user/0/com.t_arn.demoapp/files/python/user_code/app_packages/toga/handlers.py", line 55, in _handler
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:     result = handler(interface, *args, **kwargs)
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:   File "/data/user/0/com.t_arn.demoapp/files/python/user_code/app/demoapp/app.py", line 39, in handle_btn_goto1
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:     self.box.remove(self.box.children[0])
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:   File "/data/user/0/com.t_arn.demoapp/files/python/user_code/app_packages/toga/widgets/base.py", line 135, in remove
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python:     self._impl.remove_child(child._impl)
2021-02-10 08:00:53.875 5279-5279/com.t_arn.demoapp E/Python: AttributeError: 'Box' object has no attribute 'remove_child'

So, unfortunately, your workaround does not cover both mobile platforms, which means that in my app code I would need to treat iOS specifically with if platform == 'iOS'