Check if event has any listeners?

Is it possible to detect if event has any listeners? (I need to dispose my event provider object, if nobody needs it)

是否可以检测事件是否有任何听众? (如果没有人需要,我需要处理我的事件提供者对象)

3 个解决方案

#1

Assume the class is in a 3rd party library and it can't be modified:

假设该类位于第三方库中,并且无法修改:

    public class Data
    {
       public event EventHandler OnSave;
       //other members
    }

In your program:

在你的程序中:

    Data d = new Data();
    d.OnSave += delegate { Console.WriteLine("event"); };
    var handler = typeof(Data).GetField("OnSave", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(d) as Delegate;

    if (handler == null)
    {
        //no subscribers
    }
    else
    {
        var subscribers = handler.GetInvocationList();
        //now you have the subscribers
    }

#2

You can check if event is != null.

您可以检查事件是否为!= null。

By the way, in C# you need this check each time you raise an event:

顺便说一下,在C#中,每次举办活动时都需要进行检查:

if (TheEvent != null) {
    TheEvent(this, e);
}

and the reason is exactly to check if the event has any listener.

原因是检查事件是否有任何监听器。

EDIT
Since you can't access TheEvent from outside the class, you could implement a method that does the check:

编辑因为您无法从类外部访问TheEvent,您可以实现一个执行检查的方法:

public class TheClass {
    public bool HasEventListeners() {
        return TheEvent != null;
    }
}

#3

void Main()
{
    Console.WriteLine(ContainsOnSomethingEvent()); // false
    OnSomething += (o,e) => {};
    Console.WriteLine(ContainsOnSomethingEvent()); // true
}
EventHandler mOnSomething;

event EventHandler OnSomething {
    add { mOnSomething = (EventHandler)EventHandler.Combine(mOnSomething, value);   }
    remove { mOnSomething = (EventHandler)EventHandler.Remove(mOnSomething, value); }
}

public bool ContainsOnSomethingEvent() {
    return mOnSomething != null && mOnSomething.GetInvocationList().Length > 0;
}

#1