EventBus实现 - 发布订阅 - XML加载

受到CQRS的影响，写了个EventBus，能实现发布订阅模式执行event，在DDD模型中，可以使用如下代码触发事件：

EventBus bus = EventBus.Instance();
bus.Publish(new OrderAddedEvent());

解决方案结构图如下，很简单易懂：

xml事件配置代码sample如下（1个event可以定义多个订阅者，如下）：

<?xml version="1.0" encoding="utf-8" ?>
<Events>
  <Event>
    <PublishEvent>ConsoleApplication2.code.Events.OrderAddedEvent</PublishEvent>
    <SubscribedEvents>
      <SubscribedEvent>ConsoleApplication2.code.EventHandlers.OrderAddedEventHandler_CachePrepare</SubscribedEvent>
        <SubscribedEvent>ConsoleApplication2.code.EventHandlers.OrderAddedEventHandler_PDFGenerate</SubscribedEvent>
    </SubscribedEvents>
  </Event>
  <Event>
    <PublishEvent>ConsoleApplication2.code.Events.OrderDeletedEvent</PublishEvent>
    <SubscribedEvents>
      <SubscribedEvent>ConsoleApplication2.code.EventHandlers.OrderDeletedEventHandler_NotifyClient</SubscribedEvent>
      <SubscribedEvent>ConsoleApplication2.code.EventHandlers.OrderDeletedEventHandler_RemovCache</SubscribedEvent>
    </SubscribedEvents>
  </Event>
</Events>

我们先来定义Event：

public class BaseEvent         //空的，不需要实现其他方法
{
}
public class OrderAddedEvent : BaseEvent      //订单已经加入，触发的event
{
}
public class OrderDeletedEvent : BaseEvent     //订单已经删除，触发的event
{
        public Guid OrderId { get; set; }
        public OrderDeletedEvent(Guid orderId)
        {
            this.OrderId = orderId;
        }
}

定义事件的处理程序：

public interface IEventHandler<T>
        where T : BaseEvent
{
        void Handle(T evt);
}
public class OrderDeletedEventHandler_NotifyClient : IEventHandler<OrderDeletedEvent>
{
        public void Handle(OrderDeletedEvent evt)
        {
            Console.WriteLine("[Order deleted] Notified.");
        }
}

上面2个步骤很简单，只是简单的定义事件、事件处理程序，要怎样才能触发事件处理程序并且做成可配置的方式呢？请看下面代码即可：

private static Dictionary<Type, List<Type>> eventMapping = new Dictionary<Type, List<Type>>();

XElement root=XElement.Load(System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "EventBus.xml"));  //这个xml文件需要设置为一直拷贝到程序目录中
foreach (var evt in root.Elements("Event"))
{
       List<Type> eventHandlers = new List<Type>();

       Type publishEventType = Type.GetType(evt.Element("PublishEvent").Value);
       foreach (var subscritedEvt in evt.Elements("SubscribedEvents"))
            foreach (var concreteEvt in subscritedEvt.Elements("SubscribedEvent"))
                eventHandlers.Add(Type.GetType(concreteEvt.Value));

       eventMapping[publishEventType] = eventHandlers; //加入Dictionary中
}

再来上发布代码：

        public void Publish(BaseEvent evt)
        {
            var result = from tb in eventMapping
                         where tb.Key.Equals(evt.GetType())
                         select tb;

            foreach (KeyValuePair<Type, List<Type>> t in result.ToList())
            {
                foreach (Type tt in t.Value)
                {
                    Type targetType = tt;
                    MethodInfo mi=targetType.GetMethod("Handle"); //这个Handle文本字符串，必须和IEventHandler<T>中定义的方法一致
                    if(mi==null)
                        continue;

                    object o = Activator.CreateInstance(targetType);  //new实例
                    mi.Invoke(o, new object[] { evt });               //调用方法，并且传入事件参数
                }
            }
        }