using System;

​

public class Program

{

    public static void Main(string[] commandString)

    {

        using (var subscriber = new EventSubscriber(Console.WriteLine))     

        {

            subscriber.EmulateEventBeingRaised();

            subscriber.EmulateEventBeingRaised();

            subscriber.EmulateEventBeingRaised();

            subscriber.EmulateEventBeingRaised();

            subscriber.EmulateEventBeingRaised();

        }

        Console.WriteLine();

        Console.ReadLine();

    }

    public class EventSubscriber : IDisposable

    {

        event Action<string> CertainEvent;

        Action<string> _callback;

        int counter;

        public EventSubscriber(Action<string> callback)

        {

            if (callback == null) throw new ArgumentNullException("callback");

            _callback = callback;

            CertainEvent += _callback;

        }

        public void Dispose()

        {

            Console.WriteLine(CertainEvent.GetInvocationList().Length);

            CertainEvent -= _callback;

            Console.WriteLine(CertainEvent == null);

        }

        public void EmulateEventBeingRaised() 

        {

            counter++;

            if (CertainEvent != null)

            {

                CertainEvent("Hey, we did it, " + counter + " times...");

            }

        }

    }

}