另请参阅https://flutter.io/flutter-for-android/#how-do-i-listen-to-android-
activity-lifecycle-events

您可以收听不活动，已暂停和已分离的内容。这可能为时过早，但通常最好是过早且频繁地进行一些清理，而不是根本不做：

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

根据2019年11月4日的拉取请求，该枚举AppLifecycleState.suspending被重命名为AppLifecycleState.detached。如果您使用的Flutter版本低于1.12，则仍必须使用AppLifecycleState.suspending。