# 生命周期API部分（这部分只有flutter端，无原生实现）

## 1. 全局监听API

一般在main阶段就可以添加一个全局观察者
```dart
void main() {
  ///添加全局生命周期监听类
  PageVisibilityBinding.instance.addGlobalObserver(AppLifecycleObserver());
  runApp(MyApp());
}
```

`AppLifecycleObserver`的具体实现如下
```dart
///全局生命周期监听示例
class AppLifecycleObserver with GlobalPageVisibilityObserver {
  @override
  void onBackground(Route route) {
    super.onBackground(route);
    print("AppLifecycleObserver - onBackground");
  }

  @override
  void onForeground(Route route) {
    super.onForeground(route);
    print("AppLifecycleObserver - onForground");
  }

  @override
  void onPagePush(Route route) {
    super.onPagePush(route);
    print("AppLifecycleObserver - onPagePush");
  }

  @override
  void onPagePop(Route route) {
    super.onPagePop(route);
    print("AppLifecycleObserver - onPagePop");
  }

  @override
  void onPageHide(Route route) {
    super.onPageHide(route);
    print("AppLifecycleObserver - onPageHide");
  }

  @override
  void onPageShow(Route route) {
    super.onPageShow(route);
    print("AppLifecycleObserver - onPageShow");
  }
}
```

## 2.单个页面的监听
```dart
///单个生命周期示例
class LifecycleTestPage extends StatefulWidget {
  const LifecycleTestPage({Key key}) : super(key: key);

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

class _LifecycleTestPageState extends State<LifecycleTestPage>
    with PageVisibilityObserver {
  @override
  void onBackground() {
    super.onBackground();
    print("LifecycleTestPage - onBackground");
  }

  @override
  void onForeground() {
    super.onForeground();
    print("LifecycleTestPage - onForeground");
  }

  @override
  void onPageHide() {
    super.onPageHide();
    print("LifecycleTestPage - onPageHide");
  }

  @override
  void onPageShow() {
    super.onPageShow();
    print("LifecycleTestPage - onPageShow");
  }

  @override
  void initState() {
    super.initState();

    ///请在didChangeDependencies中注册而不是initState中
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();

    ///注册监听器
    PageVisibilityBinding.instance.addObserver(this, ModalRoute.of(context));
  }

  @override
  void dispose() {
    ///移除监听器
    PageVisibilityBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return ...;
  }
}
```

### 额外说明
 - 在页面层级，没有`push`事件和`pop`事件，初始化逻辑请直接写在`initState`，卸载逻辑请写在`dispose`中即可

 - `onPageShow`对标Android`onResume`，iOS `viewDidAppear`
 - `onPageHide`对标Android`onStop`，iOS `viewDidDisappear`