using System;

public class Program

{

    public delegate void Test(int x, object y);

    public class A

    {

        public event Test TestEvent;

        public void StartTest(int x)

        {

            Console.WriteLine("A.StartTest " + x.ToString());

            //TestEvent(x, null);

        }

        public void X()

        {

            if(TestEvent == null)

            {

                Console.WriteLine("null TestEvent");

                return;

            }

            TestEvent(1, null);

        }

    }

    public static void Main()

    {

        var a = new A();

        Ex(a);

        a.TestEvent -= (x, y) => a.StartTest(x);

        a.X();

    }

    public static void Ex(A a)

    {

        a.TestEvent += (x, y) => a.StartTest(x);

    }

}