EventBus实现 - 发布订阅 - XML加载

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
}
}
}

运行效果图如下：



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