using System;

​

public class Program

{

​

public delegate void CallBackNotification(string message);

​

public class CallBackClient

{

    public void DoWork(CallBackNotification callbackPointer)

    {

        Console.WriteLine("Work started");

        if(callbackPointer != null)

            callbackPointer("Work is done");

    }

}

public class TestCallBack

{

    public void TestCallBackMethod()

    {

        CallBackNotification callbackPointer = new CallBackNotification(DoWorkAfterCallBack);

        CallBackClient myClient = new CallBackClient();

        myClient.DoWork(callbackPointer);

    }

    public void DoWorkAfterCallBack(string message)

    {

        Console.WriteLine(message);

    }

}

public static void Main()

{

    TestCallBack test = new TestCallBack();

    test.TestCallBackMethod();

}

​

}