Subclassing and Hooking with Visual Basic: Harnessing the Full Power of VB/VB.NET

by Stephen Teilhet

Overview

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.

Product Details

ISBN-13:	9781491932681
Publisher:	O'Reilly Media, Incorporated
Publication date:	06/15/2001
Sold by:	Barnes & Noble
Format:	eBook
Pages:	706
File size:	3 MB

About the Author

Stephen Teilhet earned a degree in electrical engineering but soon afterwards began writing software for the Windows platform. For the last eight years, he has worked for several consulting firms on a wide range of projects, specializing in Visual Basic, Visual C++, MTS, COM, MSMQ, and SQL Server. Stephen currently works for Compuware Numega Labs in Nashua, New Hampshire, where he is immersed in the Microsoft .NET technologies.

Table of Contents

	Preface	xi
I.	Introducing Subclassing and Hooking	1
1.	Introduction	3
	Subclassing	4
	The Window Hooking Mechanism	5
	Tools to Aid Us in Our Efforts	6
	A Word of Warning	16
2.	Windows System-Specific Information	17
	Inside a Windows Application	18
	Inside the Windows Messaging System	42
	Performance Considerations	47
3.	The Basics of Subclassing and Hooks	48
	What Is Subclassing?	48
	What Are Hooks?	67
II.	Subclassing and Superclassing	81
4.	Subclassing	83
	The AddressOf Operator	83
	Some Subclassing Tips	90
	Instance Subclassing: An Example	91
	Global Subclassing	112
	Summary of Key Points in Subclassing	131
5.	Subclassing the Windows Common Dialog Boxes	133
	How Common Dialog Box Subclassing Works	135
	Using the Resource	150
	Creating the Subclassing Application	154
	Subclassing Common Dialog Boxes Other Than Open and Save As	175
	Problems Subclassing the Find and Replace Common Dialogs	191
6.	ActiveX Controls and Subclassing	195
	Subclassing a Third-Party ActiveX Control	195
	Subclassing an ActiveX Control Created in VB	196
	Subclassing a UserControl from Within a VB-Created ActiveX Control	202
	Creating an ActiveX Control That Subclasses Other Windows	209
7.	Superclassing	218
	What Is Superclassing?	218
	How the Superclassing Example Works	223
	Peering into the Superclassing Application with Spy++	243
8.	Debugging Techniques for Subclassing	247
	Where to Start	247
	Microsoft Tools	252
	NuMega's SmartCheck	254
III.	Hooking	267
9.	WH_CALLWNDPROC	269
	How WH_CALLWNDPROC Works	269
	A Thread-Specific Example	279
	Caveats	285
10.	WH_CALLWNDPROCRET	286
	How WH_CALLWNDPROCRET Works	286
	A Thread-Specific Example	289
	Caveats	296
11.	WH_GETMESSAGE	298
	How WH_GETMESSAGE Works	298
	A Thread-Specific Example	304
	Caveats	312
12.	WH_KEYBOARD and WH_KEYBOARD_LL	314
	How Keyboard Messaging Operates	314
	Description of Hooks	318
	A Thread-Specific Example	324
	A System-Wide Example	330
	A Low-Level Hook Example	335
	Caveats	339
13.	WH_MOUSE and WH_MOUSE_LL	341
	How Mouse Messaging Operates	341
	Description of Hooks	345
	Location of This Hook in the System	351
	A Single-Thread Example	351
	A System-Wide Hook Example	355
	Caveats	365
14.	WH_FOREGROUNDIDLE	366
	Description	366
	Location of This Hook in the System	367
	Background Processing Example	369
	Caveats	374
15.	WH_MSGFILTER	376
	Description	376
	A Thread-Specific Example	384
	Caveats	389
16.	WH_SYSMSGFILTER	391
	Description	391
	A System-Wide Example	393
	Caveats	399
17.	WH_SHELL	400
	Description	400
	Location of This Hook in the System	408
	A Thread-Specific Example	409
	Caveats	416
18.	WH_CBT	418
	Description	420
	A Thread-Specific Example	429
	Caveats	443
19.	WH_JOURNALRECORD	444
	Description	444
	The Macro Recorder Example	450
	Caveats	457
20.	WH_JOURNALPLAYBACK	458
	Description	458
	The Macro Recorder/Playback Example	462
	Caveats	470
21.	WH_DEBUG	472
	Description	472
	A Thread-Specific Example	475
	Some WH_DEBUG Scenarios	485
	Caveats	487
IV.	The .NET Platform	489
22.	Subclassing .NET WinForms	491
	What Is a WinForm?	491
	Instance Subclassing	494
	Subclassing a Control	511
	Superclassing	514
	Superclassing a Control	519
	Intercepting Keystrokes in a WinForm	522
	Behind the Scenes with Spy++	529
23.	Implementing Hooks in VB.NET	534
	Hooks and VB.NET	534
	Delegates	535
	Implementing the WH_KEYBOARD Hook	540
	Implementing the WH_MOUSE Hook	547
V.	Appendixes	555
A.	Messages	557
B.	API Functions	601
C.	Structures and Constants	630
	Index	663