binding_observer.dart

import 'package:flutter/material.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();

  runApp(const App());
}

class App extends StatelessWidget {
  const App({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      initialRoute: '/',
      routes: {
        '/': (context) => const HomeScreen(),
        '/settings': (context) => const SettingsScreen(),
      },
    );
  }
}

class HomeScreen extends StatefulWidget {
  const HomeScreen({Key? key}) : super(key: key);

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> with WidgetsBindingObserver {
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    print('HomeScreen Init');
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    super.didChangeAppLifecycleState(state);
    print(state);
  }

  @override
  void dispose() {
    print('HomeScreen Dispose');
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        automaticallyImplyLeading: false,
        title: const Text('Home'),
        actions: [
          IconButton(
            onPressed: () => Navigator.of(context).pushNamed('/settings'),
            icon: const Icon(Icons.settings),
          ),
        ],
      ),
    );
  }
}

class SettingsScreen extends StatelessWidget {
  const SettingsScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        automaticallyImplyLeading: false,
        leading: const BackButton(),
        title: const Text('Settings'),
      ),
    );
  }
}