全局監聽路由堆棧變化

老孟導讀：不少時候咱們須要監聽路由堆棧的變化，這樣能夠自定義路由堆棧、方便分析異常日誌等。

監聽路由堆棧的變化使用 RouteObserver ，首先在 MaterialApp 組件中添加 navigatorObservers：

void main() {
  runApp(MyApp());
}

RouteObserver<PageRoute> routeObserver = RouteObserver<PageRoute>();

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      ...
      navigatorObservers: [routeObserver],
      home: HomePage(),
    );
  }
}

監聽頁面設置以下：

class ARouteObserverDemo extends StatefulWidget {
  @override
  _RouteObserverDemoState createState() => _RouteObserverDemoState();
}

class _RouteObserverDemoState extends State<ARouteObserverDemo> with RouteAware {

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    routeObserver.subscribe(this, ModalRoute.of(context));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        alignment: Alignment.center,
        child: RaisedButton(
          child: Text('A RouteObserver'),
          onPressed: () {
            Navigator.of(context).pushNamed('/BRouteObserver');
          },
        ),
      ),
    );
  }

  @override
  void dispose() {
    super.dispose();
    routeObserver.unsubscribe(this);
  }

  @override
  void didPush() {
    final route = ModalRoute.of(context).settings.name;
    print('A-didPush route: $route');
  }

  @override
  void didPopNext() {
    final route = ModalRoute.of(context).settings.name;
    print('A-didPopNext route: $route');
  }

  @override
  void didPushNext() {
    final route = ModalRoute.of(context).settings.name;
    print('A-didPushNext route: $route');
  }

  @override
  void didPop() {
    final route = ModalRoute.of(context).settings.name;
    print('A-didPop route: $route');
  }

}

其中 didPush、didPushNext、didPopNext、didPop 爲路由堆棧變化的回調。

從 A 頁面跳轉到 ARouteObserverDemo 頁面，日誌輸出以下：

flutter: A-didPush route: /ARouteObserver

進入此頁面只調用了 didPush。

從 ARouteObserverDemo 頁面跳轉到 BRouteObserverDemo 頁面（同 ARouteObserverDemo 頁面，設置了監聽），日誌輸出以下：

flutter: A-didPushNext route: /ARouteObserver
flutter: B-didPush route: /BRouteObserver

先調用了 ARouteObserverDemo 頁面的 didPushNext，而後調用了 BRouteObserverDemo 頁面的 didPush。

從 BRouteObserverDemo 頁面執行 pop 返回 ARouteObserverDemo 頁面，日誌輸出以下：

flutter: A-didPopNext route: /ARouteObserver
flutter: B-didPop route: /BRouteObserver

先調用了 ARouteObserverDemo 頁面的 didPopNext，而後調用了 BRouteObserverDemo 頁面的 didPop。

上面的案例僅僅是頁面級別的路由堆棧變化，若是想知道整個應用程序路由堆棧變化如何處理？

一種方法是寫一個監聽路由堆棧的基類，全部頁面繼承此基類。此方法對源代碼的侵入性很是高。

還有一種方法是自定義 RouteObserver，繼承RouteObserver並重寫其中的方法：

class MyRouteObserver<R extends Route<dynamic>> extends RouteObserver<R> {
  @override
  void didPush(Route route, Route previousRoute) {
    super.didPush(route, previousRoute);
    print('didPush route: $route,previousRoute:$previousRoute');
  }

  @override
  void didPop(Route route, Route previousRoute) {
    super.didPop(route, previousRoute);
    print('didPop route: $route,previousRoute:$previousRoute');
  }

  @override
  void didReplace({Route newRoute, Route oldRoute}) {
    super.didReplace(newRoute: newRoute, oldRoute: oldRoute);
    print('didReplace newRoute: $newRoute,oldRoute:$oldRoute');
  }

  @override
  void didRemove(Route route, Route previousRoute) {
    super.didRemove(route, previousRoute);
    print('didRemove route: $route,previousRoute:$previousRoute');
  }

  @override
  void didStartUserGesture(Route route, Route previousRoute) {
    super.didStartUserGesture(route, previousRoute);
    print('didStartUserGesture route: $route,previousRoute:$previousRoute');
  }

  @override
  void didStopUserGesture() {
    super.didStopUserGesture();
    print('didStopUserGesture');
  }
}

使用：

void main() {
  runApp(MyApp());
}

MyRouteObserver<PageRoute> myRouteObserver = MyRouteObserver<PageRoute>();

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      navigatorObservers: [myRouteObserver],
      initialRoute: '/A',
      home: APage(),
    );
  }
}

此時從 A 頁面 跳轉到 B 頁面，日誌輸出以下：

flutter: didPush route: MaterialPageRoute<dynamic>(RouteSettings("/B", 來自A), animation: AnimationController#6d429(▶ 0.000; for MaterialPageRoute<dynamic>(/B))),previousRoute:MaterialPageRoute<dynamic>(RouteSettings("/A", null), animation: AnimationController#e60f7(⏭ 1.000; paused; for MaterialPageRoute<dynamic>(/A)))

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