在C#中使用Lambda进行一次拍摄的事件 [英] One shot events using Lambda in C#

问题描述

我发现自己经常做这种事情:-

I find myself doing this sort of thing quite often:-

 EventHandler eh = null;  //can't assign lambda directly since it uses eh
 eh = (s, args) =>
 {
     //small snippet of code here

     ((SomeType)s).SomeEvent -= eh;
 }
 variableOfSomeType.SomeEvent += eh;

基本上，我只想附加一个事件处理程序以侦听该事件的一个镜头，此后我不再想要保持连接状态.通常，代码快照"只是一行.

Basically I only want to attach an event handler to listen for one shot from the event, I no longer want to stay attached after that. Quite often that "snippert of code" is just one line.

我的头脑有点麻木，我确定必须做点什么，所以我不需要重复所有这些开销.请记住，EventHandler很可能是EventHandler<T>.

My mind is going a bit numb, I'm sure there must be something I can do so I don't need to repeat all this overhead. Bear in mind that EventHandler may well be EventHandler<T>.

有什么想法可以整理代码的重复部分，并将代码段留在Lambda中吗?

Any ideas how I can tidy up the repeative part of the code and just leave the snippet in a Lambda?

推荐答案

您可以使用反射:

public static class Listener {

  public static void ListenOnce(this object eventSource, string eventName, EventHandler handler) {
    var eventInfo = eventSource.GetType().GetEvent(eventName);
    EventHandler internalHandler = null;
    internalHandler = (src, args) => {
      eventInfo.RemoveEventHandler(eventSource, internalHandler);
      handler(src, args);
    };
    eventInfo.AddEventHandler(eventSource, internalHandler);
  }

  public static void ListenOnce<TEventArgs>(this object eventSource, string eventName, EventHandler<TEventArgs> handler) where TEventArgs : EventArgs {
    var eventInfo = eventSource.GetType().GetEvent(eventName);
    EventHandler<TEventArgs> internalHandler = null;
    internalHandler = (src, args) => {
      eventInfo.RemoveEventHandler(eventSource, internalHandler);
      handler(src, args);
    };
    eventInfo.AddEventHandler(eventSource, internalHandler);
  }

}

像这样使用它:

variableOfSomeType.ListenOnce("SomeEvent", 
  (s, args) => Console.WriteLine("I should print only once!"));

variableOfSomeType.ListenOnce<InterestingEventArgs>("SomeOtherEvent", 
  (s, args) => Console.WriteLine("I should print only once!"));

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