详解Flutter中的数据传递

// 1.InheritedWidget，我们定义了一个继承自它的新类 CountContainer,里面存放需要共享的数据
//然后，我们将计数器状态 count 属性放到 CountContainer 中，并提供了一个 of 方法方便其子 Widget 在 Widget 树中找到它。
//最后，我们重写了 updateShouldNotify 方法，这个方法会在 Flutter 判断 InheritedWidget 是否需要重建，
class CountContainer extends InheritedWidget {
 static CountContainer of(BuildContext context) =>
   context.dependOnInheritedWidgetOfExactType<CountContainer>();
 final _InheritedWidgetHomeState mode;
 final Function() function;

 CountContainer(
   {Key key,
   @required this.mode,
   @required this.function,
   @required Widget child})
   : super(key: key, child: child);

 @override
 bool updateShouldNotify(covariant InheritedWidget oldWidget) {
  return this != oldWidget;
 }
}



// 2. 通过构建方法，把数据放到 InheritedWidget中
class _InheritedWidgetHomeState<InheritedWidgetHome> extends State {
 int count = 0;

 void _incrementCounter() => setState(() {
  count  ;
 });

 @override
 Widget build(BuildContext context) {
  return CountContainer(
   mode: this,
   function: _incrementCounter,
   child: CountWidget(),
  );
 }
}

// 3. 在子 widget 通过 CountContainer.of方法，获取到自定义的 InheritedWidget，并从中取得共享的数据
class CountWidget extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  CountContainer state = CountContainer.of(context);
  return Scaffold(
   appBar: AppBar(
    title: Text("InheritedWidget demo"),
   ),
   body: Text("current count is ${state.mode.count}"),
   floatingActionButton: FloatingActionButton(
    child: Icon(Icons.add),
    onPressed: state.function,
   ),
  );
 }
}

event_bus: 2.0.0

//建立公共的event bus
EventBus eventBus = EventBus();

class CustomEvent {
 String msg;

 CustomEvent(this.msg);
}

class _EventBusPager1State extends State {
 String message = "原来的数据";
 StreamSubscription subscription;

 @override
 void initState() {
  subscription = eventBus.on<CustomEvent>().listen((event) {
   setState(() {
    message = event.msg;
   });
  });
  super.initState();
 }

 @override
 Widget build(BuildContext context) {
  return Scaffold(
   appBar: AppBar(
    title: Text("EventBusPager1"),
   ),
   body: Center(
    child: Text(message),
   ),
   floatingActionButton: FloatingActionButton(
    child: Icon(Icons.open_in_browser),
    onPressed: () => Navigator.push(
      context, MaterialPageRoute(builder: (context) => EventBusPager2())),
   ),
  );
 }

 @override
 void dispose() {
  subscription.cancel();
  super.dispose();
 }
}

class EventBusPager2 extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  return Scaffold(
   appBar: AppBar(
    title: Text("EventBusPager2"),
   ),
   body: Center(
    child: Text("EventBusPager1"),
   ),
   floatingActionButton: FloatingActionButton(
    child: Icon(Icons.send),
    onPressed: () {
     eventBus.fire(CustomEvent("data from page 2"));
     Navigator.pop(context);
    },
   ),
  );
 }
}