Question

I have always wondered how delegates can be useful and why shall we use them? Other then being type safe and all those advantages in Visual Studio Documentation, what are real world uses of delegates.

I already found one and it’s very targeted.

using System;

namespace HelloNamespace {

    class Greetings{
    public static void DisplayEnglish() {
            Console.WriteLine("Hello, world!");
    }
    public static void DisplayItalian() {
             Console.WriteLine("Ciao, mondo!");
    }
    public static void DisplaySpanish() {
             Console.WriteLine("Hola, imundo!");
         }
    }

    delegate void delGreeting();

    class HelloWorld {
        static void Main(string [] args) {

    int iChoice=int.Parse(args[0]);
    delGreeting [] arrayofGreetings={
             new delGreeting(Greetings.DisplayEnglish),
             new delGreeting(Greetings.DisplayItalian),
             new delGreeting(Greetings.DisplaySpanish)};

    arrayofGreetings[iChoice-1]();
         }
    }
}

But this doesn’t show me exactly the advantages of using delegates rather than a conditional “If … { }” that parses the argument and run the method.

Does anyone know why it’s better to use delegate here rather than “if … { }”. Also do you have other examples that demonstrate the usefulness of delegates.

Thanks!

Answer 1

The most common real-world everyday use of delegates that I can think of in C# would be event handling. When you have a button on a WinForm, and you want to do something when the button is clicked, then what you do is you end up registering a delegate function to be called by the button when it is clicked.

All of this happens for you automatically behind the scenes in the code generated by Visual Studio itself, so you might not see where it happens.

A real-world case that might be more useful to you would be if you wanted to make a library that people can use that will read data off an Internet feed, and notify them when the feed has been updated. By using delegates, then programmers who are using your library would be able to have their own code called whenever the feed is updated.