Closing the app leaks an IntentReceiver because of onListen

[nanobug]

Maybe there should be some 'shutdown' api to make a unregister call for the stateStreamHandler?

[AgainPsychoX]

As far as I know Flutter does not have API for disposing platform code on app termination. Problem is, there is no way to use onDestroy method of Activity (flutter/flutter#21982).

There is possibility to detect application life-cycle, including suspending and resuming - which potentially could be used in future 🤔 . I think it would cause onStateChanged and similar streams to be closed every time app goes suspended, so user will need to reopen the stream(s).

Further plans:

• Add private function dispose or something in Android platform plugin class to be invoked,
• Use Lifecycle or similar exposed by Flutter.
• Detect certain life-cycle states (even maybe ON_DESTROY) and call the dispose function,
• Dispose whatever needs to be disposed.

Added Good First Issue since it isn't that much hard to achieve, there are my suggestion about where/how to start working on it and this is not that critical issue.

[AgainPsychoX]

Flutter plugin registry exposes addViewDestroyListener which allows the library take a part in onDestroy of the application... I think I was blind, I did not see it...

Commit with fix landing in few minutes on develop branch, so closing for now.