Advanced C#

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If you want to study C# in depth, keep reading. This ten-part series covers advanced topics to help you sharpen your skills in the language. It is excerpted from chapter four of C# 3.0 in a Nutshell, Third Edition, A Desktop Quick Reference, written by Joseph Albahari and Ben Albahari (O'Reilly; ISBN: 0596527578). Copyright © 2007 O'Reilly Media, Inc. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media.

In this chapter, we cover advanced C# topics that build on concepts explored in previous chapters. You should read the first four sections sequentially; you can read the remaining sections in any order.

Delegates

A delegate dynamically wires up a method caller to its target method. There are two aspects to a delegate: type and instance. A delegate type defines a protocol to which the caller and target will conform, comprising a list of parameter types and a return type. A delegate instance refers to one (or more) target methods conforming to that protocol.

A delegate instance literally acts as a delegate for the caller: the caller invokes the delegate, and then the delegate calls the target method. This indirection decouples the caller from the target method.

A delegate type declaration is preceded by the keyworddelegate, but otherwise it resembles an (abstract) method declaration. For example:

  delegate int Transformer (int x);

To create a delegate instance, you can assign a method to a delegate variable:

  class Test
  {
    static void Main()
    {
      Transformer t = Square;    // create delegate instance
      int result = t(3);           // invoke delegate
      Console.WriteLine (result);
    }
    static int Square (int x) { return x * x; }
  }

Invoking a delegate is just like invoking a method (since the delegate’s purpose is merely to provide a level of indirection):

  t(3);

This statement:

  Transformer t = Square;

is shorthand for:

  Transformer t = new Transformer(Square);

A delegate is similar to a callback, a general term that captures constructs such as C function pointers.

Next: Writing Plug-in Methods with Delegates >>
 

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