Activity

• Represents a single focused thing the user can do.
• In Android, you can override methods from the Activity to capture lifecycle methods for the activity itself, or register ActivityLifecycleCallbacks on the Application.
• In Flutter, you have neither concept, but you can instead listen to lifecycle events by hooking into the WidgetsBinding observer and listening to the didChangeAppLifecycleState() change event.
• An example of how to observe the lifecycle status of the containing activity:.

  Import 'package:flutter/widgets.dart';
  
  class LifecycleWatcher extends StatefulWidget {
    @override
    _LifecycleWatcherState createState() => _LifecycleWatcherState();
  }
  
  class _LifecycleWatcherState extends State<LifecycleWatcher> with WidgetsBindingObserver {
    AppLifecycleState _lastLifecycleState;
  
    @override
    void initState() {
      super.initState();
      WidgetsBinding.instance.addObserver(this);
    }
  
    @override
    void dispose() {
      WidgetsBinding.instance.removeObserver(this);
      super.dispose();
    }
  
    @override
    void didChangeAppLifecycleState(AppLifecycleState state) {
      setState(() {
        _lastLifecycleState = state;
      });
    }
  
    @override
    Widget build(BuildContext context) {
      if (_lastLifecycleState == null)
        return Text('This widget has not observed any lifecycle changes.', textDirection: TextDirection.ltr);
  
      return Text('The most recent lifecycle state this widget observed was: $_lastLifecycleState.',
          textDirection: TextDirection.ltr);
    }
  }
  
  void main() {
    runApp(Center(child: LifecycleWatcher()));
  }

The observable lifecycle events are:.