Subclassing and Hooking with Visual Basic
Subclassing & Hooking with Visual Basic offers developers a unique way to customize Windows behavior. Windows is a message-based system. Every action you request creates one or more messages to carry out the action. These messages are passed between objects and carry with them information that gives the recipient more detail on how to interpret and act upon the message. With Subclassing and the Windows hooking mechanism ("hooks"), you can manipulate, modify, or even discard messages bound for other objects within the operating system, in the process changing the way the system behaves. What kinds of results can you achieve using the power of subclassing and hooking? Here are just a few of the possibilities:
* Determine when a window is being activated or deactivated and respond to this change.
* Display descriptions of menu items as the mouse moves across them.
* Disallow a user to move or resize a window.
* Determine where the mouse cursor is and respond accordingly.
* Determine when the display resolution has been changed.
* Monitor the system for a low system resource condition.
* Modify or disallow keystrokes sent to a window or a control.
* Create an automated testing application.
* Determine when an application is idle.
Along with this power comes responsibility; Windows is very unforgiving if subclassing and hooking are used incorrectly. Subclassing & Hooking with Visual Basic demonstrates the various techniques for intercepting messages bound for one or more windows or controls: the intercepted message can be left in its original state or modified; afterwards, the message can be sent to its original destination or discarded. For both VB 6 and VB.NET developers, Subclassing & Hooking with Visual Basic opens up a wealth of possibilities that ordinarily would be completely unavailable, or at least not easy to implement.
From the Author
I decided to write this book when I noticed that there was no single place you could go to learn about subclassing and hooking. These two subjects were geared towards the more advanced C++ developers. Unfortunately, there was not much information to help the Visual Basic developer to understand how, when, where, and why to use these techniques.
In doing some research I came to the realization that not many Visual Basic developers had a solid grasp of these techniques. These techniques were being misused and even underused. Developers were creating incredibly complex, and hard to maintain code, code that could be greatly simplified if the programmer had only taken advantage of subclassing, hooking, or even both techniques used in tandem. This book is meant to not only to teach subclassing and hooking techniques, but also to be a single resource in which developers can get information and answers to their questions about these techniques.
This book is geared towards the Visual Basic developer who wants a better understanding of subclassing and hooking as well as how to incorporate these techniques into their projects. You need not be an advanced Visual Basic developer to learn how to effectively use subclassing and hooking. Although, many of the Win32 API function will need to be utilized in order to write subclassing and hooking applications and, therefore, a good knowledge of the Win32 API functions and how they are used within Visual Basic is necessary.
In understanding subclassing and hooks, you must delve deep into the internals of the Window’s operating system. This deeper understanding of Windows allows you not only to gain an understanding of subclassing and hooking, but also to learn more about the messaging system, which is the heart of the Windows operating system. The beginning of this book lays a solid foundation that will bring the beginning or intermediate developer up to speed on these topics.