eventsource.cs

public class EventHandlerSource : IEventSource
	{
		readonly RuntimeEvent @event;
		readonly object owner;
		readonly Delegate eventHandler;
		static readonly MethodInfo HandleOwnerEventMethodInfo = typeof(EventHandlerSource)
			.GetMethod("HandleOwnerEvent", BindingFlags.NonPublic | BidningFlags.Instance);

		event EventHandler handler;
		int subscriptions = 0;

		public EventHandlerSource (RuntimeEvent @event, object owner)
		{
			this.@event = @event;
			this.owner = owner;

			eventHandler = @event.CreateDelegate(this, HandleOwnerEventMethodInfo);			
		}

		void HandleOwnerEvent(object sender, EventArgs args) {
			if (Handler != null) {
				Handler(sender, args);
			}
		}

		public void SetEnabled (bool enabled)
		{
			if (SetEnabledAction != null)
				SetEnabledAction (Owner, enabled);
		}

		public object Owner { get { return owner; } }

		public Action<object, bool> SetEnabledAction { get; set; }

		public event EventHandler Handler {
			add { 
				handler += value; 
				if (subscriptions == 0) 
					this.@event.AddEventHandler(Owner, eventHandler);
				subscriptions++;
			}
			remove { 
				handler -= value; 
				subscriptions--;
				if (subscriptions == 0) 
					this.@event.RemoveEventHandler(Owner, eventHandler);				
			}
		}
	}