didChangeAppLifecycleState method
Called when the system puts the app in the background or returns the app to the foreground.
An example of implementing this method is provided in the class-level documentation for the WidgetsBindingObserver class.
This method exposes notifications from SystemChannels.lifecycle.
See also:
- AppLifecycleListener, an alternative API for responding to application lifecycle changes.
Implementation
@override
Future<void> didChangeAppLifecycleState(AppLifecycleState state) async {
  switch (state) {
    case AppLifecycleState.resumed:
      await resumeCallBack();
      break;
    case AppLifecycleState.inactive:
    case AppLifecycleState.paused:
      await pauseCallBack();
      break;
    case AppLifecycleState.detached:
      await suspendingCallBack();
      break;
    case AppLifecycleState.hidden:
      break;
  }
}