Delegates and Callbacks

Question

Does the term callback in the context of delegates mean ,"a delegate delegating it works to another delegate inorder to finish some task" ?

Example :(Based on my understanding,I have implemented a callback,correct me if it is wrong)

namespace Test
{
    public delegate string CallbackDemo(string str);  

    class Program
    {
        static void Main(string[] args)
        {
            CallbackDemo handler = new CallbackDemo(StrAnother);
            string substr = Strfunc(handler);
            Console.WriteLine(substr);
            Console.ReadKey(true);
        }

        static string Strfunc(CallbackDemo callback)
        {
           return callback("Hello World");   
        }

        static string StrAnother(string str)
        {
            return str.Substring(1, 3).ToString();
        }
    }
}

Please provide examples as necessary.

Answer 1

Your example is a good start, but it is incorrect. You don't make a new delegate in the method, it's used in the declaration of an event in the class. See this modified example of your code:

namespace Test
{
    //In this case, this delegate declaration is like specifying a specific kind of function that must be used with events.
    public delegate string CallbackDemo(string str);
    class Program
    {
        public static event CallbackDemo OnFoobared;
        static void Main(string[] args)
        {
            //this means that StrAnother is "subscribing" to the event, in other words it gets called when the event is fired
            OnFoobared += StrAnother;
            string substr = Strfunc();
            Console.WriteLine(substr);
            Console.ReadKey(true);
            //this is the other use of delegates, in this case they are being used as an "anonymous function". 
            //This one takes no parameters and returns void, and it's equivalent to the function declaration 
            //'void myMethod() { Console.WriteLine("another use of a delegate"); }'
            Action myCode = delegate
            {
                Console.WriteLine("another use of a delegate");
            };
            myCode();
            Console.ReadKey(true);
            //the previous 4 lines are equivalent to the following however this is generally what you should use if you can
            //its called a lambda expression but it's basically a way to toss arbitrary code around
            //read more at http://www.developer.com/net/csharp/article.php/3598381/The-New-Lambda-Expressions-Feature-in-C-30.htm or 
            //http://stackoverflow.com/questions/167343/c-lambda-expression-why-should-i-use-this
            Action myCode2 = () => Console.WriteLine("a lambda expression");
            myCode2();
            Console.ReadKey(true);
        }

        static string Strfunc()
        {
            return OnFoobared("a use of a delegate (with an event)");
        }
        static string StrAnother(string str)
        {
            return str.Substring(1, 3).ToString();
        }
    }
}

I've only scratched the surface here; search stack overflow for "delegate c#" and "lambda expression c#" for lots more!