Question

So I’m a little bit confused about delegates in C#…. what do they do and how are they useful? I’ve read a few tutorials, and I don’t really get exactly what they’re supposed to do (everyone relates them to function pointers in C, and I’ve never programmed in C).

So… what do delegates do? What’s a scenario in which I should use them? How would I then use them?

Answer 1

Delegates are sort of like objects that represent a method call. One useful way they can be used are as callbacks. For example, imagine you have a method that does something asynchronous, and you want the caller to be able to specify what they want to happen once it completes (Action is a type of delegate):

public void DoSomething(Action whatToDoWhenDone)
{
    // Your code

    // See how the delegate is called like a method
    whatToDoWhenDone();
}

A user of DoSomething can now specify the callback as a parameter:

public void AnotherMethod()
{
    DoSomething(ShowSuccess); // ShowSuccess will be called when done
}

public void ShowSuccess()
{
    Console.WriteLine("Success!");
}

You can also use lamba expressions as a shorter way of writing your delegate:

public void AnotherMethod()
{
    DoSomething(() => Console.WriteLine("Success!"));
    // Also DoSomething(delegate() { Console.WriteLine("Success!"); });
}

Callbacks are far from the only use cases for delegates. Hopefully this shows you some of their power: the ability to have code to be executed as a variable.