Flutter 根界面退出的时候（即是应用退出），不会触发deactivate/dispose方法 / 监听返回按钮

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    print('----------------！！！！！build  111！！！！----------------');
    return Scaffold(
        body: GestureDetector(
      behavior: HitTestBehavior.opaque,
      onTap: () {
        Navigator.of(context).push(new MaterialPageRoute(builder: (_) => SecondPage()));
      },
      child: Container(
        color: Colors.red,
      ),
    ));
  }

  @override
  void deactivate() {
    super.deactivate();
    print('----------------！！！！！deactivate  111！！！！----------------');
  }

  @override
  void dispose() {
    print('----------------！！！！！dispose  111！！！！----------------');
    super.dispose();
  }
}

I/flutter (18058): ----------------！！！！！build  111！！！！----------------

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  Future<bool> _onBackPressed() {
    return showDialog(
        context: context,
        builder: (context) => AlertDialog(
              title: Text('确定退出程序吗?'),
              actions: <Widget>[
                FlatButton(
                  child: Text('暂不'),
                  onPressed: () => Navigator.pop(context, false),
                ),
                FlatButton(
                  child: Text('确定'),
                  onPressed: () => Navigator.pop(context, true),
                ),
              ],
            ));
  }

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: _onBackPressed,
      child: Scaffold(
        appBar: AppBar(
          title: Text('title'),
        ),
        body: Center(
          child: Text('exit'),
        ),
      ),
    );
  }
}