class AppLifePage extends StatefulWidget {
  CEAppLifePage({Key key}) : super(key: key);
  @override
  _AppLifePageState createState() => _AppLifePageState();
}
//  實現WidgetsBindingObserver觀察者
class _AppLifePageState extends State<AppLifePage> with WidgetsBindingObserver{
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this); //添加觀察者
  }
  @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: $state");
    switch (state) {
        case AppLifecycleState.resumed:
          print('應用程序可見且響應用戶輸入。');
          break;
        case AppLifecycleState.paused:
          print('應用程序不可見且無法響應用戶輸入，運行在后臺。');
          break;
        case AppLifecycleState.inactive: 
          print('應用程序處于非激活狀態，無法響應用戶輸入。'); 
          break;
        case AppLifecycleState.detached: 
          print('應用程序仍寄存在Flutter引擎上，但與平臺 View 分離。'); 
          break;
      }
  }
  //  當前系統改變了一些訪問性活動的回調
  @override
  void didChangeAccessibilityFeatures() {
    super.didChangeAccessibilityFeatures();
    print("didChangeAccessibilityFeatures");
  }
  //  低內存回調
  @override
  void didHaveMemoryPressure() {
    super.didHaveMemoryPressure();
    print("didHaveMemoryPressure");
  }
  //  用戶本地設置變化時調用，如系統語言改變
  @override
  void didChangeLocales(List<Locale> locale) {
    super.didChangeLocales(locale);
    print("didChangeLocales");
  }
  //  應用尺寸改變時回調，例如旋轉
  @override
  void didChangeMetrics() {
    super.didChangeMetrics();
    Size size = WidgetsBinding.instance.window.physicalSize;
    print("didChangeMetrics  ：寬：${size.width} 高：${size.height}");
  }
  //  系統切換主題時回調
  @override
  void didChangePlatformBrightness() {
    super.didChangePlatformBrightness();
    print("didChangePlatformBrightness");
  }
  //  文字系數變化
  @override
  void didChangeTextScaleFactor() {
    super.didChangeTextScaleFactor();
    print(
        "didChangeTextScaleFactor  ：${WidgetsBinding.instance.window.textScaleFactor}");
  }
  @override
  void dispose() {
    super.dispose();
    WidgetsBinding.instance.removeObserver(this); //  銷毀觀察者
  }
}