DDD(六)【领域事件与事件总线】

谈谈它

终于有些眉目了，搜刮了很多牛人的资料，英文的，中文的，民国文的，终于小有成就了，同时也做了个ＤＥＭＯ，领域事件这东西好，但需要你明白它之后才会说好，而对于明白领域事件这件事来说，它的门槛有点高，居然花了我三天的时间才把它搞定，嗨！

占占给它的定义

领域事件：Domain Event,是针对某个业务来说的，或者说针对某个聚合的业务来说的，例如订单生成这种业务，它可以同时对应一种事件，比如叫做OrderGeneratorEvent，而你的零散业务可能随时会变，加一些业务，减一些业务，而对于订单生成这个事件来说，它是唯一不变的，而我们需要把这些由产生订单而发生变化的事情拿出来，而拿出来的这些业务就叫做＂领域事件＂．其中的领域指的就是订单生成这个聚合；而事件指的就是那些零散业务的统称．

它的主要几个抽象

在面向对象的编程世界里，做这种事情我们需要几个抽象：

领域对象事件标示：（标示接口，接口的一种，用来约束一批对象）IEvent

领域对象的处理方法，行为：（需要让那些零散的模块重写的方法，起个听起来熟悉的名字，叫它handle吧）IEventHandler＝＞Handle

事件总线：事件处理核心类，承载了事件的发布，订阅与取消订阅的逻辑，EventBus

某个领域对象：为了实现某个业务，而创建的实体类，它里面有事件所需要的数据，它继承了IEvent

某个领域对象的事件：它是一个事件处理类，它实现了IEventHandler，它所处理的事情需要在Handle里去完成

我的Demo的实现

一　结果图：

二　核心类：

IEvent接口，标示接口往往都是空的，呵呵

    /// <summary>/// 事件实体基类/// </summary>public interface IEvent{}

IEventHandler接口，只有一个行为方法Handle

    /// <summary>/// 事件处理接口/// </summary>/// <typeparam name="TEvent">继承IEvent对象的事件源对象</typeparam>public interface IEventHandler<TEvent>where TEvent : IEvent{/// <summary>/// 处理程序/// </summary>/// <param name="evt"></param>void Handle(TEvent evt);}

EventBus是实现事件的核心，在这版里，它支持异步事件机制,使用Task实现，所以它需要运行在.net4.5平台之上

 　 /// <summary>/// 事件总线/// 发布与订阅处理逻辑/// 核心功能代码/// </summary>public class EventBus{private EventBus() { }private static EventBus _eventBus = null;private readonly object sync = new object();/// <summary>/// 对于事件数据的存储，目前采用内存字典/// </summary>private static Dictionary<Type, List<object>> eventHandlers = new Dictionary<Type, List<object>>();/// <summary>// checks if the two event handlers are equal. if the event handler is an action-delegated, just simply// compare the two with the object.Equals override (since it was overriden by comparing the two delegates. Otherwise,// the type of the event handler will be used because we don't need to register the same type of the event handler// more than once for each specific event./// </summary>private readonly Func<object, object, bool> eventHandlerEquals = (o1, o2) =>{var o1Type = o1.GetType();var o2Type = o2.GetType();if (o1Type.IsGenericType &&o1Type.GetGenericTypeDefinition() == typeof(ActionDelegatedEventHandler<>) &&o2Type.IsGenericType &&o2Type.GetGenericTypeDefinition() == typeof(ActionDelegatedEventHandler<>))return o1.Equals(o2);return o1Type == o2Type;};/// <summary>/// 初始化空的事件总件/// </summary>public static EventBus Instance{get{return _eventBus ?? (_eventBus = new EventBus());}}/// <summary>/// 通过ＸＭＬ文件初始化事件总线，订阅信自在ＸＭＬ里配置/// </summary>/// <returns></returns>public static EventBus InstanceForXml(){if (_eventBus == null){XElement root = XElement.Load(System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "EventBus.xml"));foreach (var evt in root.Elements("Event")){List<object> handlers = new List<object>();Type publishEventType = Type.GetType(evt.Element("PublishEvent").Value);foreach (var subscritedEvt in evt.Elements("SubscribedEvents"))foreach (var concreteEvt in subscritedEvt.Elements("SubscribedEvent"))handlers.Add(Type.GetType(concreteEvt.Value));eventHandlers[publishEventType] = handlers;}_eventBus = new EventBus();}return _eventBus;}#region 事件订阅&取消订阅，可以扩展/// <summary>/// 订阅事件列表/// </summary>/// <param name="type"></param>/// <param name="subTypeList"></param>public void Subscribe<TEvent>(IEventHandler<TEvent> eventHandler)where TEvent : class, IEvent{lock (sync){var eventType = typeof(TEvent);if (eventHandlers.ContainsKey(eventType)){var handlers = eventHandlers[eventType];if (handlers != null){if (!handlers.Exists(deh => eventHandlerEquals(deh, eventHandler)))handlers.Add(eventHandler);}else{handlers = new List<object>();handlers.Add(eventHandler);}}elseeventHandlers.Add(eventType, new List<object> { eventHandler });}}/// <summary>/// 订阅事件实体/// </summary>/// <param name="type"></param>/// <param name="subTypeList"></param>public void Subscribe<TEvent>(Action<TEvent> eventHandlerFunc)where TEvent : class, IEvent{Subscribe<TEvent>(new ActionDelegatedEventHandler<TEvent>(eventHandlerFunc));}public void Subscribe<TEvent>(IEnumerable<IEventHandler<TEvent>> eventHandlers)where TEvent : class, IEvent{foreach (var eventHandler in eventHandlers)Subscribe<TEvent>(eventHandler);}/// <summary>/// 取消订阅事件/// </summary>/// <param name="type"></param>/// <param name="subType"></param>public void Unsubscribe<TEvent>(IEventHandler<TEvent> eventHandler)where TEvent : class, IEvent{lock (sync){var eventType = typeof(TEvent);if (eventHandlers.ContainsKey(eventType)){var handlers = eventHandlers[eventType];if (handlers != null&& handlers.Exists(deh => eventHandlerEquals(deh, eventHandler))){var handlerToRemove = handlers.First(deh => eventHandlerEquals(deh, eventHandler));handlers.Remove(handlerToRemove);}}}}public void Unsubscribe<TEvent>(IEnumerable<IEventHandler<TEvent>> eventHandlers)where TEvent : class, IEvent{foreach (var eventHandler in eventHandlers)Unsubscribe<TEvent>(eventHandler);}public void Unsubscribe<TEvent>(Action<TEvent> eventHandlerFunc)where TEvent : class, IEvent{Unsubscribe<TEvent>(new ActionDelegatedEventHandler<TEvent>(eventHandlerFunc));}#endregion#region 事件发布/// <summary>/// 发布事件，支持异步事件/// </summary>/// <typeparam name="TEvent"></typeparam>/// <param name="evnt"></param>public void Publish<TEvent>(TEvent evnt)where TEvent : class, IEvent{if (evnt == null)throw new ArgumentNullException("evnt");var eventType = evnt.GetType();if (eventHandlers.ContainsKey(eventType)&& eventHandlers[eventType] != null&& eventHandlers[eventType].Count > 0){var handlers = eventHandlers[eventType];foreach (var handler in handlers){var eventHandler = handler as IEventHandler<TEvent>;if (eventHandler.GetType().IsDefined(typeof(HandlesAsynchronouslyAttribute), false)){Task.Factory.StartNew((o) => eventHandler.Handle((TEvent)o), evnt);}else{eventHandler.Handle(evnt);}}}}public void Publish<TEvent>(TEvent evnt, Action<TEvent, bool, Exception> callback, TimeSpan? timeout = null)where TEvent : class, IEvent{if (evnt == null)throw new ArgumentNullException("evnt");var eventType = evnt.GetType();if (eventHandlers.ContainsKey(eventType) &&eventHandlers[eventType] != null &&eventHandlers[eventType].Count > 0){var handlers = eventHandlers[eventType];List<Task> tasks = new List<Task>();try{foreach (var handler in handlers){var eventHandler = handler as IEventHandler<TEvent>;if (eventHandler.GetType().IsDefined(typeof(HandlesAsynchronouslyAttribute), false)){tasks.Add(Task.Factory.StartNew((o) => eventHandler.Handle((TEvent)o), evnt));}else{eventHandler.Handle(evnt);}}if (tasks.Count > 0){if (timeout == null)Task.WaitAll(tasks.ToArray());elseTask.WaitAll(tasks.ToArray(), timeout.Value);}callback(evnt, true, null);}catch (Exception ex){callback(evnt, false, ex);}}elsecallback(evnt, false, null);}#endregion}

一个具体的领域对象，它继承IEvent

    /// <summary>/// 添加订单的事件/// </summary>public class OrderGeneratorEvent : IEvent{public int OrderID { get; set; }}

一个为OrderGeneratorEvent工作的领域事件，它用来为客户发邮件

　  /// <summary>/// 发邮件功能/// </summary>public class OrderAddedEventHandler_SendEmail : IEventHandler<OrderGeneratorEvent>{public void Handle(OrderGeneratorEvent evt){Console.WriteLine("Order_Number:{0},Send a Email.", evt.OrderID);}}

下面看一个主程序：

   static void Main(string[] args){EventBus.Instance.Subscribe(new OrderAddedEventHandler_SendEmail());var entity = new OrderGeneratorEvent { OrderID = 1 };Console.WriteLine("生成一个订单，单号为{0}", entity.OrderID);EventBus.Instance.Publish(entity);Console.ReadKey();}

下面是运行结果：