Check if event is registered

Question

If I have the classic ways to register and unregister events (+= -=), is there also a way to see whether something is registered right now?

Let's say I have 2 methods which can register on one Timer. If something has already registered at .Elapsed, I do not want anything else to register (and do not want something to register multiple times).

Is there any way to look up which methods are registered at the moment to a specific event?

Answer 1

If you really want such behaviour, I think the best option is to use the overload the add{} and remove{} functionality of the event.

public class Foo
{

   private EventHandler<ElapsedEventArgs> _elapsed;

   public EventHandler<ElapsedEventArgs> Elapsed
   {
       add
       {
           if( _elapsed == null )
               _elapsed += value;
           else
               throw new InvalidOperationException ("There is already an eventhandler attached to the Elapsed event.");
       }
       remove
       {
           _elapsed -= value;
       }
   }

}

Answer 2

You can use GetInvocationList() and get the count in turn