简介
事件总线是对发布-订阅模式的一种实现,是一种集中式事件处理机制,允许不同的组件之间进行彼此通信而又不需要相互依赖,达到一种解耦的目的。
实现事件总线
EventBus维护一个事件的字典,发布者、订阅者在事件总线中获取事件实例并执行发布、订阅操作,事件实例负责维护、执行事件处理程序。流程如下:
定义事件基类
事件实例需要在事件总线中注册,定义一个基类方便事件总线进行管理,代码如下:
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/// <summary> /// 事件基类 /// </summary> public abstract class EventBase{ } |
事件实例需要管理、执行已经注册的事件处理程序,为了适应不同的事件参数使用泛型参数,不允许此类实例化。代码如下:
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/// <summary> /// 泛型事件 /// </summary> /// <typeparam name="T"></typeparam> public abstract class PubSubEvent<T> : EventBase where T : EventArgs { protected static readonly object locker = new object (); protected readonly List<Action< object , T>> subscriptions = new List<Action< object , T>>(); public void Subscribe(Action< object , T> eventHandler) { lock (locker) { if (!subscriptions.Contains(eventHandler)) { subscriptions.Add(eventHandler); } } } public void Unsubscribe(Action< object , T> eventHandler) { lock (locker) { if (subscriptions.Contains(eventHandler)) { subscriptions.Remove(eventHandler); } } } public virtual void Publish( object sender, T eventArgs) { lock (locker) { for ( int i = 0; i < subscriptions.Count; i++) { subscriptions[i](sender, eventArgs); } } } } |
定义事件参数基类
事件参数基类继承EventArgs,使用泛型参数适应不同的参数类型,不允许此类实例化。代码如下:
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/// <summary> /// 泛型事件参数 /// </summary> /// <typeparam name="T"></typeparam> public abstract class PubSubEventArgs<T> : EventArgs { public T Value { get ; set ; } } |
定义EventBus
EventBus只提供事件实例的管理,具体事件处理程序的执行由事件实例自己负责。为了使用方便,构造函数有自动注册事件的功能,在有多个程序集时可能会有bug。代码如下:
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/// <summary> /// 事件总线 /// </summary> class EventBus { private static EventBus _default; private static readonly object locker = new object (); private Dictionary<Type, EventBase> eventDic = new Dictionary<Type, EventBase>(); /// <summary> /// 默认事件总线实例,建议只使用此实例 /// </summary> public static EventBus Default { get { if (_default == null ) { lock (locker) { // 如果类的实例不存在则创建,否则直接返回 if (_default == null ) { _default = new EventBus(); } } } return _default; } } /// <summary> /// 构造函数,自动加载EventBase的派生类实现 /// </summary> public EventBus() { Type type = typeof (EventBase); Type typePubSub = typeof (PubSubEvent<>); Assembly assembly = Assembly.GetAssembly(type); List<Type> typeList = assembly.GetTypes() .Where(t => t != type && t != typePubSub && type.IsAssignableFrom(t)) .ToList(); foreach (var item in typeList) { EventBase eventBase = (EventBase)assembly.CreateInstance(item.FullName); eventDic.Add(item, eventBase); } } /// <summary> /// 获取事件实例 /// </summary> /// <typeparam name="TEvent">事件类型</typeparam> /// <returns></returns> public TEvent GetEvent<TEvent>() where TEvent : EventBase { return (TEvent)eventDic[ typeof (TEvent)]; } /// <summary> /// 添加事件类型 /// </summary> /// <typeparam name="TEvent"></typeparam> public void AddEvent<TEvent>() where TEvent : EventBase , new () { lock (locker) { Type type = typeof (TEvent); if (!eventDic.ContainsKey(type)) { eventDic.Add(type, new TEvent()); } } } /// <summary> /// 移除事件类型 /// </summary> /// <typeparam name="TEvent"></typeparam> public void RemoveEvent<TEvent>() where TEvent : EventBase, new () { lock (locker) { Type type = typeof (TEvent); if (eventDic.ContainsKey(type)) { eventDic.Remove(type); } } } } |
使用事件总线
事件及事件参数
使用事件总线前,需要定义好事件及事件参数。在使用时,发布者、订阅者也必须知道事件类型及事件参数类型。代码如下:
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/// <summary> /// 泛型事件实现-TestAEvent,重写事件的触发逻辑 /// </summary> public class TestAEvent: PubSubEvent<TestAEventArgs> { public override void Publish( object sender, TestAEventArgs eventArgs) { lock (locker) { for ( int i = 0; i < subscriptions.Count; i++) { var action= subscriptions[i]; Task.Run(() => action(sender, eventArgs)); } } } } /// <summary> /// 泛型事件参数实现-TestAEventArgs /// </summary> public class TestAEventArgs : PubSubEventArgs< string > { } /// <summary> /// 泛型事件实现-TestBEvent /// </summary> public class TestBEvent : PubSubEvent<TestBEventArgs> { } /// <summary> /// 泛型事件参数实现-TestBEventArgs /// </summary> public class TestBEventArgs : PubSubEventArgs< int > { } |
注:TestAEvent中重写了事件发布的逻辑,每个事件在任务中执行。
定义发布者
发布者通过事件总线获取事件实例,在实例上发布事件,代码如下:
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class Publisher { public void PublishTeatAEvent( string value) { EventBus.Default.GetEvent<TestAEvent>().Publish( this , new TestAEventArgs() { Value=value}); } public void PublishTeatBEvent( int value) { EventBus.Default.GetEvent<TestBEvent>().Publish( this , new TestBEventArgs() { Value = value }); } } |
#d8b0a89d237cd0dc8a8b345eb3c5bd2c#
定义订阅者
订阅者通过事件总线获取事件实例,在实例上订阅事件,代码如下:
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class ScbscriberA { public string Name { get ; set ; } public ScbscriberA( string name) { Name = name; EventBus.Default.GetEvent<TestAEvent>().Subscribe(TeatAEventHandler); } public void TeatAEventHandler( object sender, TestAEventArgs e) { Console.WriteLine(Name+ ":" +e.Value); } } class ScbscriberB { public string Name { get ; set ; } public ScbscriberB( string name) { Name = name; EventBus.Default.GetEvent<TestBEvent>().Subscribe(TeatBEventHandler); } public void Unsubscribe_TeatBEvent() { EventBus.Default.GetEvent<TestBEvent>().Unsubscribe(TeatBEventHandler); } public void TeatBEventHandler( object sender, TestBEventArgs e) { Console.WriteLine(Name + ":" + e.Value); } } |
实际使用
代码如下:
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class Program { static void Main( string [] args) { Publisher publisher = new Publisher(); ScbscriberA scbscriberA = new ScbscriberA( "scbscriberA" ); ScbscriberB scbscriberB1 = new ScbscriberB( "scbscriberB1" ); ScbscriberB scbscriberB2 = new ScbscriberB( "scbscriberB2" ); publisher.PublishTeatAEvent( "test" ); publisher.PublishTeatBEvent(123); scbscriberB2.Unsubscribe_TeatBEvent(); publisher.PublishTeatBEvent(12345); Console.ReadKey(); } } |
运行结果:
scbscriberB1:123
scbscriberB2:123
scbscriberA:test
scbscriberB1:12345
总结
这个事件总线只提供了基础功能,实现的发布者和订阅者的解耦,发布者、订阅者只依赖事件不互相依赖。
感觉我对事件总线的理解还有点不足,欢迎大家来一起讨论!
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原文链接:https://www.cnblogs.com/timefiles/p/CsharpEventBase.html