Flutter笔记十之event_bus

event_bus的主要作用是各组件间的通信，能有效的分离事件发送方和接收方(解耦)，类似通知。

导入event_bus

可以通过添加依赖的方式导入，因为代码不多，我就直接创建个文件把代码复制进去了，下面是event_bus版本号2.0.0的源代码

import 'dart:async';

/// Dispatches events to listeners using the Dart [Stream] API. The [EventBus]
/// enables decoupled applications. It allows objects to interact without
/// requiring to explicitly define listeners and keeping track of them.
///
/// Not all events should be broadcasted through the [EventBus] but only those of
/// general interest.
///
/// Events are normal Dart objects. By specifying a class, listeners can
/// filter events.
///
class EventBus {
  StreamController _streamController;

  /// Controller for the event bus stream.
  StreamController get streamController => _streamController;

  /// Creates an [EventBus].
  ///
  /// If [sync] is true, events are passed directly to the stream's listeners
  /// during a [fire] call. If false (the default), the event will be passed to
  /// the listeners at a later time, after the code creating the event has
  /// completed.
  EventBus({bool sync = false})
      : _streamController = StreamController.broadcast(sync: sync);

  /// Instead of using the default [StreamController] you can use this constructor
  /// to pass your own controller.
  ///
  /// An example would be to use an RxDart Subject as the controller.
  EventBus.customController(StreamController controller)
      : _streamController = controller;

  /// Listens for events of Type [T] and its subtypes.
  ///
  /// The method is called like this: myEventBus.on<MyType>();
  ///
  /// If the method is called without a type parameter, the [Stream] contains every
  /// event of this [EventBus].
  ///
  /// The returned [Stream] is a broadcast stream so multiple subscriptions are
  /// allowed.
  ///
  /// Each listener is handled independently, and if they pause, only the pausing
  /// listener is affected. A paused listener will buffer events internally until
  /// unpaused or canceled. So it's usually better to just cancel and later
  /// subscribe again (avoids memory leak).
  ///
  Stream<T> on<T>() {
    if (T == dynamic) {
      return streamController.stream as Stream<T>;
    } else {
      return streamController.stream.where((event) => event is T).cast<T>();
    }
  }

  /// Fires a new event on the event bus with the specified [event].
  ///
  void fire(event) {
    streamController.add(event);
  }

  /// Destroy this [EventBus]. This is generally only in a testing context.
  ///
  void destroy() {
    _streamController.close();
  }
}

创建event_bus对象(发送端)

final EventBus eventBus = EventBus();

监听相应的响应事件(接收端，可以放在initState()中)

_event = eventBus.on<类型>().listen((event) {
  //接收数据并按需更新界面
  setState(() { });
}); 

销毁event_bus对象(接收端，放在dispose()中)

_event.dispose();

发出事件(发送端)

eventBus.fire(传递的数据)

至此就结束了，so easy…下面是一个小demo：

//创建EventBus对象
final EventBus eventBus = EventBus();
//传递的对象
class GCUserInfo {
  GCUserInfo(this.name, this.age);
  final String name;
  final int age;
}

class EventBusApp extends StatelessWidget {
  const EventBusApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: GCHomePage(),
    );
  }
}

class GCHomePage extends StatelessWidget {
  const GCHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("EventBus"),),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            TextButton(onPressed: (){
              final userInfo = GCUserInfo("Steven", Random().nextInt(100));
              //发出事件
              eventBus.fire(userInfo);
            }, child: Text("按钮", style: TextStyle(fontSize: 18),)),
            GCText()
          ],
        ),
      ),
    );
  }
}

class GCText extends StatefulWidget {
  const GCText({Key? key}) : super(key: key);
  @override
  State<GCText> createState() => _GCTextState();
}

class _GCTextState extends State<GCText> {
  String info = "Hello world!";
  late final _event;
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    //3.监听相应类型的事件
    _event = eventBus.on<GCUserInfo>().listen((event) {
      setState(() {
        info = "${event.name}-----${event.age}";
      });
    });
  }
  @override
  Widget build(BuildContext context) {
    return Text(info, style: TextStyle(fontSize: 18),);
  }

  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    _event.dispose();
  }
}

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