另请参见https://flutter.io/flutter-for-android/#how-do-i-listen-to-android-activity-lifecycle-events
你可以监听非活动、暂停和断开的状态。这可能有点太早，但通常来说，太早和频繁地做一些清理总比什么都不做好：

WidgetsBinding.instance.addObserver(LifecycleEventHandler(
    detachedCallBack: () async => widget.appController.persistState(),
    resumeCallBack: () async {
      _log.finest('resume...');
    }));

class LifecycleEventHandler extends WidgetsBindingObserver {
  LifecycleEventHandler({this.resumeCallBack, this.detachedCallBack});
  final FutureVoidCallback resumeCallBack;
  final FutureVoidCallback detachedCallBack;
//  @override
//  Future<bool> didPopRoute()
//  @override
//  void didHaveMemoryPressure()
  @override
  Future<void> didChangeAppLifecycleState(AppLifecycleState state) async {
    switch (state) {
      case AppLifecycleState.inactive:
      case AppLifecycleState.paused:
      case AppLifecycleState.detached:
        await detachedCallBack();
        break;
      case AppLifecycleState.resumed:
        await resumeCallBack();
        break;
    }
    _log.finest('''
=============================================================
               $state
=============================================================
''');
  }
//  @override
//  void didChangeLocale(Locale locale)
//  @override
//  void didChangeTextScaleFactor()
//  @override
//  void didChangeMetrics();
//  @override
//  Future<bool> didPushRoute(String route)
}

编辑

在2019年11月4日的pull request中，枚举AppLifecycleState.suspending被重命名为AppLifecycleState.detached。如果您使用的Flutter版本早于1.12，您必须仍然使用AppLifecycleState.suspending。