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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
- 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)
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
