CHookWnd v1.02

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Introduction

Welcome to CHookWnd, a freeware MFC class to support subclassing of any CWnd instance. The problem it fixes is that you cannot have 2 CWnd instances attached to the one HWND at the same time. This becomes a problem when you want to derive one of your classes from 2 base classes which are both derived from CWnd themselves. An example is, suppose you have 2 classes namely CBitmapMenuFrameWnd, which is derived from CFrameWnd and implements bitmap menus ALA Office 97, and CReBarFrameWnd, which implements command bar menus ALA IE4. When you are implementing your own CMainFrame class you then have the problem that you can only derive from one of these classes and you must copy the source from the other one into your class.

This class fixes this problem by subclassing the window before MFC gets to it using a plugin method. The code is based in part on a class developed by Paul DiLascia namely "CSubclassWnd" for the MSJ magazine.

Features

Usage

History

API Reference

Planned Enhancements

Contacting the Author

Features

• Simple and clean C++ interface. Just derive your plugin class from CHookWnd and override one virtual function to implement your functionality.
• Multi-thread safe class.
• Unicode enabled, supports linking to MFC statically and all code compiles cleanly at warning level 4.

Usage

• To use the class in your code include hookwnd.cpp in your project and #include hookwnd.h in which ever of your modules needs to make calls to the class.
• Derive your class from CHookWnd and override the virtual function WindowProc() just like you did when you wrote your first Windows SDK app.
• Install the plugin class by calling the Hook function in the class you want to subclass.
• Your code will need to include MFC either statically or dynamically.
• You will also need to have afxmt.h in your precompiled header. The code will warn you if you haven't this set up.
• To see the code in action have a look at the sample app which installs 3 hooks, one to report on mouse messages, another to report on keyboard messages and a third one just for good luck.

History

V1.0 (25 February 1999)

• Initial public release.

V1.01 (29th March 1999)

• Minor update to remove some unnecessary comments from the code.

V1.02 (10th May 1999)

• Minor update to fix a small bug in the demo app. No changes to the actual HookWnd code itself.

API Reference

The API consists of the following member functions of the class CHookWnd

CHookWnd::CHookWnd
CHookWnd::~CHookWnd
CHookWnd::Hook
CHookWnd::UnHook
CHookWnd::Default
CHookWnd::WindowProc
CHookWnd::IsHooked
CHookWnd::FirstInChain
CHookWnd::LastInChain
CHookWnd::MiddleOfChain
CHookWnd::SizeOfHookChain

CHookWnd::CHookWnd

BOOL CHookWnd::CHookWnd();

Remarks:
Standard C++ constructor.

CHookWnd::~CHookWnd

CHookWnd::~CHookWnd();

Remarks:
Standard C++ destructor.

CHookWnd::Hook

void CHookWnd::Hook(CWnd* pWnd);

Parameters:

• pWnd -- The CWnd instance which you want to subclass.

Remarks:
Call this member function to subclass the HWND currently subclassed by the MFC CWnd instance "pWnd". Messages will be routed to the WindowProc method of this instance prior to being passed of to any other installed CHookWnd's in the chain before eventually being routed back to standard MFC message maps..

See Also:
CHookWnd::UnHook

CHookWnd::UnHook

void CHookWnd::UnHook();

Remarks:
Removes this instance from the chain of hooks which are handling the subclassing.

See Also:
CHookWnd::Hook

CHookWnd::Default

LRESULT CHookWnd::Default();

Return Value:
The standard LRESULT which window procedures return. The actual value will depend on the message sent.

Remarks:
You can call this function in your derived WindowProc if you want to continue routing of the message. This will pass the message on to any other CHookWnd's in the chain and eventually back to MFC and your message maps.

CHookWnd::WindowProc

virtual LRESULT CHookWnd::WindowProc(UINT nMsg, WPARAM wParam, LPARAM lParam);

Return Value:
The standard LRESULT which window procedures return. The actual value will depend on the message sent.

Parameters:

• nMsg -- Specifies the Windows message to be processed.
• wParam -- Provides additional information used in processing the message. The parameter value depends on the message.
• lParam -- Provides additional information used in processing the message. The parameter value depends on the message.

Remarks:
This is the function which you should override in your derived class to implement your plugin functionality. This would appear structured very similar to an SDK window proc. For any messages which you do not handle, you should call Default for these.

CHookWnd::IsHooked

BOOL CHookWnd::IsHooked() const;

Return Value:
TRUE if this instance is currently hooking a CWnd otherwise FALSE.

Remarks:
This function is used internally in CHookWnd as an assert in functions where you first should have call Hook.

CHookWnd::FirstInChain

BOOL CHookWnd::FirstInChain() const;

Return Value:
TRUE if this instance is the first in the chain of CHookWnd's handling subclassing otherwise FALSE.

CHookWnd::LastInChain

BOOL CHookWnd::LastInChain() const;

Return Value:
TRUE if this instance is the last in the chain of CHookWnd's handling subclassing otherwise FALSE.

CHookWnd::MiddleOfChain

BOOL CHookWnd::MiddleOfChain() const;

Return Value:
TRUE if this instance is the somewhere in the chain but is not the first or last item in it.

CHookWnd::SizeOfHookChain

int CHookWnd::SizeOfHookChain() const;

Return Value:
The number of CHookWnd's in the chain which is currently handling the subclassing.

Planned Enhancements

• Implement support for installing hooks at the end and middle of the hook chain.
• Provide a better sample app. At the moment, it's very much a test program which tests all of the functions.
• If you have any other suggested improvements, please let me know so that I can incorporate them into the next release.

Contacting the Author

PJ Naughter
Email: pjn@indigo.ie
Web: http://www.naughter.com
10th May 1999

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Hooking Anonymous 5:54 19 Jun '00   Hi, I'm coding an Add-In and want to create a child window of Visual C++ from that Add-In. Is it possible to do it using this class? I've also tried deriving my class from CHookWnd & CWnd, and there are ambiguities. I don't completely understand how this class is used with windows that I create Sign In·View Thread·PermaLink 1.75/5 (3 votes) rc=5 (Access Denied) when attempting hook of IExplorer Window Mark Findlay 9:27 20 May '00   I am probably going about this all wrong, but I am trying to hook my browser window and receiving a rc=5 from the SetWindowLong() function call within the HookWindow() function. I get the browser window by performing a FindWindow() on the browser class and caption identified by Spy++. I then pass this CWnd* to the HookWindow() function. Is the browser window somehow protected against this type of hook Sign In·View Thread·PermaLink 2.00/5 (2 votes) Also available in MSJ! Shanker 15:05 16 Mar '00   This has already been covered in considerable detail in the March 1997 issue of MSJ, in the excellent series "More Fun With MFC: DIBs, Palettes, Subclassing and a Gamut of Goodies, Part II" by author Paul DiLascia. Having said that, this is a great technique and belongs in the grab bag of every MFC programmer! Thanks for reviving this technique Sign In·View Thread·PermaLink 2.00/5 (1 vote)

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