原生实现三步曲：事件总线通常实现了订阅者模式，订阅者模式包含发布者和订阅者两种角色。

a.抽象类的定义

  1. //发布者
  2. abstract class MyPublisher {
  3.   void post<T>(T event);
  4. }
  5. //订阅者
  6. typedef MySubscriber<T> = void Function(T event);
  7. //抽象类继承
  8. abstract class _EventBus extends MyPublisher {
  9.   void register<T>(MySubscriber<T> subscriber);
  10.   void unregister<T>(MySubscriber<T> subscriber);
  11. }

b.接口的实现

  1. class MyEventBus implements _EventBus {
  2.   //私有构造函数
  3.   MyEventBus._internal();
  5.   //保存单例
  6.   static MyEventBus _singleton = MyEventBus._internal();
  8.   //工厂构造函数
  9.   factory MyEventBus()=> _singleton;
  11.   List<Function> subscribers = new List();
  13.   @override
  14.   register<T>(MySubscriber<T> subscriber) {
  15.     if (!subscribers.contains(subscriber)) {
  16.       subscribers.add(subscriber);
  17.     }
  18.   }
  20.   @override
  21.   unregister<T>(MySubscriber<T> subscriber) {
  22.     if (subscribers.contains(subscriber)) {
  23.       subscribers.remove(subscriber);
  24.     }
  25.   }
  27.   @override
  28.   post<T>(T event) {
  29.     var ints = subscribers.whereType<MySubscriber<T>>();
  30.     ints?.forEach((subscriber) => subscriber?.call(event));
  31.   }
  32. }

c.用法
场景：点击按钮，使得页面数字加一

  1. //定义事件A
  2. class EventA {int count = 0;}
  3. //按钮的点击
  5. var event = EventA();
  6. void _onTap() {
  7.   event.count++;
  8.   MyEventBus().post(event);
  9. }
  10. //定阅者初始化
  11. @override
  12. void initState() {
  13.   super.initState();
  14.   _subscriber = (EventA: event) => setState(() => _count = event.count);
  15.  //注册
  16.   MyEventBus().register<EventA>(_subscriber);
  17. }

Pub上的插件库： Github地址 — EventBus

  1. class GlobalHelper {
  2.   //私有构造函数
  3.   GlobalHelper._internal();
  5.   //保存单例
  6.   static GlobalHelper _singleton = GlobalHelper._internal();
  8.   //工厂构造函数
  9.   factory GlobalHelper()=> _singleton;
  11.   static EventBus eventBus = EventBus(sync: true);
  12. }

自定义event事件

  1. //可以添加需要的属性值
  2. class MyEvent {
  3.   MyEvent();
  4. }

自定义的事件监听

  1. GlobalHelper.eventBus.on<MyEvent>().listen((event) async {
  2.   //do something
  3. });

事件的触发或发布

  1. GlobalHelper.eventBus.fire(MyEvent());

这样整个事件的广播机制就完成了。

EventBus中的实现机制

  1. /// Dispatches events to listeners using the Dart [Stream] API. The [EventBus]
  2. /// enables decoupled applications. It allows objects to interact without
  3. /// requiring to explicitly define listeners and keeping track of them.
  4. ///
  5. /// Not all events should be broadcasted through the [EventBus] but only those of
  6. /// general interest.
  7. ///
  8. /// Events are normal Dart objects. By specifying a class, listeners can
  9. /// filter events.

主要是用到了dart中的Stream： 

  1. StreamController _streamController;

关于Stream可以看下一篇文章介绍