Check if event has any listeners?

Is i开发者_开发知识库t possible to detect if event has any listeners? (I need to dispose my event provider object, if nobody needs it)

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

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

In your program:

    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
    }

You can check if event is != null.

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

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

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

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

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

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;
}