Building Applications and Components with Visual Basic .NET

The Callback: A Simple Design Pattern

Application software is often designed around the programming technique known as callbacks. In a callback, one part of an application sends out notifications to alert other parts of the application when something interesting has occurred. More specifically, a callback is a call from a notification source back to a method implemented by one or more handlers.

Most Visual Basic programmers are already familiar with the concept of callbacks because of the manner in which Visual Basic has always supported event handling. An event handler is a simple example of a callback method. When you write an event handler for the Click event of a command button, you are really writing the implementation for a callback method. ...