import 'package:flutter/material.dart';

void main() => runApp(LifecycleDemo());

// リスト 5.12
class LifecycleDemo extends StatefulWidget {
  const LifecycleDemo({Key? key}) : super(key: key);

  @override
  _LifecycleDemoState createState() => _LifecycleDemoState();
}

class _LifecycleDemoState extends State<LifecycleDemo>
    with WidgetsBindingObserver {
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance?.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance?.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    // print('AppLifecycleState: $state');
    if (state == AppLifecycleState.inactive ||
        state == AppLifecycleState.paused) {
      // 表示中の画像を保存する処理を記載
    }
  }

    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        title: 'Lifecycle',
        home: Scaffold(
          appBar: AppBar(
            title: const Text('Lifecycle'),
          ),
          body: Center(child: Text('ライフサイクル'))
        )
      );
    }
  }