C# 2008 Programmer's Reference

Chapter 7. Delegates and Events

Two of the most important aspects of object-oriented programming are delegates and events. A delegate basically enables you to reference a function without directly invoking the function. Delegates are often used to implement techniques called callbacks, which means that after a function has finished execution, a call is made to a specific function to inform it that the execution has completed. In addition, delegates are also used in event handling. Despite the usefulness of delegates, it is a topic that not all .NET programmers are familiar with. An event, on the other hand, is used by classes to notify clients when something of interest has happened. For example, a Button control has the Click even, which allows your program to be notified when someone clicks the button.

This chapter explores the following:

• What is a delegate?

• Using delegates

• Implementing callbacks using a delegate

• What are events?

• How to handle and implement events in your program

Delegates

In C#, a delegate is a reference type that contains a reference to a method. Think of a delegate as a pointer to a function. Instead of calling a function directly, you use a delegate to point to it and then invoke the method by calling the delegate. The following sections explain how to use a delegate and how it can help improve the responsiveness of your application.

Creating a Delegate

To understand the use of delegates, begin by looking at the conventional way of invoking a function. Consider the ...