Flutter组件生命周期和App生命周期示例解析

class AppLifePage extends StatefulWidget {
  CEAppLifePage({Key key}) : super(key: key);
  @override
  _AppLifePageState createState() => _AppLifePageState();
}
//  实现WidgetsBindingObserver观察者
class _AppLifePageState extends State<AppLifePage> with WidgetsBindingObserver{
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this); //添加观察者
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("App生命周期"),),
      body: Text('Flutter App 生命周期'),
    );
  }
  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    super.didChangeAppLifecycleState(state);
    print("didChangeAppLifecycleState: $state");
    switch (state) {
        case AppLifecycleState.resumed:
          print('应用程序可见且响应用户输入。');
          break;
        case AppLifecycleState.paused:
          print('应用程序不可见且无法响应用户输入，运行在后台。');
          break;
        case AppLifecycleState.inactive: 
          print('应用程序处于非激活状态，无法响应用户输入。'); 
          break;
        case AppLifecycleState.detached: 
          print('应用程序仍寄存在Flutter引擎上，但与平台 View 分离。'); 
          break;
      }
  }
  //  当前系统改变了一些访问性活动的回调
  @override
  void didChangeAccessibilityFeatures() {
    super.didChangeAccessibilityFeatures();
    print("didChangeAccessibilityFeatures");
  }
  //  低内存回调
  @override
  void didHaveMemoryPressure() {
    super.didHaveMemoryPressure();
    print("didHaveMemoryPressure");
  }
  //  用户本地设置变化时调用，如系统语言改变
  @override
  void didChangeLocales(List<Locale> locale) {
    super.didChangeLocales(locale);
    print("didChangeLocales");
  }
  //  应用尺寸改变时回调，例如旋转
  @override
  void didChangeMetrics() {
    super.didChangeMetrics();
    Size size = WidgetsBinding.instance.window.physicalSize;
    print("didChangeMetrics  ：宽：${size.width} 高：${size.height}");
  }
  //  系统切换主题时回调
  @override
  void didChangePlatformBrightness() {
    super.didChangePlatformBrightness();
    print("didChangePlatformBrightness");
  }
  //  文字系数变化
  @override
  void didChangeTextScaleFactor() {
    super.didChangeTextScaleFactor();
    print(
        "didChangeTextScaleFactor  ：${WidgetsBinding.instance.window.textScaleFactor}");
  }
  @override
  void dispose() {
    super.dispose();
    WidgetsBinding.instance.removeObserver(this); //  销毁观察者
  }
}