如何使用反射将事件处理程序附加到事件?

问题描述

我知道 EventInfo.AddEventHandler(...) 方法，该方法可用于将处理程序附加到事件.但是，如果我什至无法定义事件处理程序的正确签名，例如，我什至没有对处理程序预期的事件参数的引用，该怎么办?

I know about EventInfo.AddEventHandler(...) method which can be used to attach handler to an event. But what should be done if i can not even define proper signature of the event handler, as in, i don't even have reference to the event args expected by the handler?

我会用正确的代码解释问题.

I will explain the problem with the proper code.

//解决方案中所有可用的场景，零反射场景.

// Scenario when I have everything available in my solution, Zero Reflection Scenario.

internal class SendCommentsManager
{
    public void Customize(IRFQWindowManager rfqWindowManager)
    {
        rfqWindowManager.SendComment += HandleRfqSendComment;
    }

    private void HandleRfqSendComment(object sender, SendCommentEventArgs args)
    {
        args.Cancel = true;
    }
}

现在，我想通过使用反射来实现相同的目标.我已经能够弄清楚其中的大部分，但是当我将委托附加到事件时(使用 AddEventHandler)它会抛出 "Error binding to target method." 异常.

Now, I want to achieve the same objective by using reflection. I have been able to figure out most of it but when i attach a delegate to the event (using AddEventHandler) it throws "Error binding to target method." exception.

我了解此异常背后的原因，将错误的委托附加到事件.但必须有某种方法来实现这一点.

I understand the reason behind this exception, attaching a wrong delegate to an event. But there must be some way to achieve this.

 internal class SendCommentsManagerUsingReflection
 {
     public void Customize(IRFQWindowManager rfqWindowManager)
     {
         EventInfo eventInfo = rfqWindowManager.GetType().GetEvent("SendComment");
         eventInfo.AddEventHandler(rfqWindowManager, 
             Delegate.CreateDelegate(eventInfo.EventHandlerType, this, "HandleRfqSendComment"));
         //<<<<<<<<<<ABOVE LINE IS WHERE I AM GOING WRONG>>>>>>>>>>>>>>
     }

     private void HandleRfqSendComment(object sender, object args)
     {
         Type sendCommentArgsType = args.GetType();
         PropertyInfo cancelProperty = sendCommentArgsType.GetProperty("Cancel");
         cancelProperty.SetValue(args, true, null);
     }
 }

推荐答案

我认为您的代码失败了，因为 HandleRfqSendComment 是私有的.相反，您可以直接为该方法创建一个委托，而无需将其名称传递给 CreateDelegate.然后，您需要使用以下方法将委托转换为所需的类型:

I think your code is failing because the HandleRfqSendComment is private. Instead you could directly create a delegate to that method, without passing its name to CreateDelegate. You would then need to convert the delegate to the required type, using the following method :

public static Delegate ConvertDelegate(Delegate originalDelegate, Type targetDelegateType)
{
    return Delegate.CreateDelegate(
        targetDelegateType,
        originalDelegate.Target,
        originalDelegate.Method);
}

在您的代码中，您可以按如下方式使用此方法:

In your code, you could use this method as follows :

EventInfo eventInfo = rfqWindowManager.GetType().GetEvent("SendComment");
Action<object, object> handler = HandleRfqSendComment;
Delegate convertedHandler = ConvertDelegate(handler, eventInfo.EventHandlerType);
eventInfo.AddEventHandler(rfqWindowManager, convertedHandler);

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