using System;
using System.Linq;
using System.Threading;

static class Extensions
{
	public static Delegate ConvertTo(this Delegate self, Type type)
	{
		if (type == null) { throw new ArgumentNullException("type"); }
		if (self == null) { return null; }
		
		if (self.GetType() == type)
                return self;
                
		return Delegate.Combine(
			self.GetInvocationList()
				.Select(i => Delegate.CreateDelegate(type, i.Target, i.Method))
				.ToArray());
	}
	
	public static T ConvertTo<T>(this Delegate self)
	{
		return (T)(object)self.ConvertTo(typeof(T));
	}
}

public class A  { }

public class B : A {}

public delegate void MyEventHandler<in T>(object sender, T arg);

public class TheClass {
 
 	public event MyEventHandler<B> MyEvent {
 		add {
 			this._myEvent += value.ConvertTo<MyEventHandler<B>>();
 		}
 		remove {
 			this._myEvent -= value.ConvertTo<MyEventHandler<B>>();
 		}
 	}
 
	private MyEventHandler<B> _myEvent; 
	
	public void RaiseEvent(B arg)
	{
		var handler = this._myEvent;
		if(handler != null)
			handler(this, arg);
	}
 
}

class Program
{
	static void Main()
	{
		var obj = new TheClass();
		
		obj.MyEvent += new MyEventHandler<B>((sender, e) => Console.WriteLine("B handler: Hey there from {0} with {1}!", sender, e));
		obj.MyEvent += new MyEventHandler<A>((sender, e) => Console.WriteLine("A handler: Hey there from {0} with {1}!", sender, e));
		obj.MyEvent += new MyEventHandler<object>((sender, e) => Console.WriteLine("Object handler: Hey there from {0} with {1}!", sender, e));
		
		obj.RaiseEvent(new B());
	}
}