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Q32167: SuperCls.exe Demonstrates Superclassing

Article: Q32167
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.0,3.1
Operating System(s): 
Keyword(s): kbfile kbsample kb16bitonly kbGrpDSUser kbOSWin310 kbWndw kbWndwClass kbWndwProc kbOSWi
Last Modified: 24-DEC-1999

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1 
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SUMMARY
=======

SuperCls.exe is a sample application that demonstrates the concept of
superclassing control windows. Superclassing provides the same capabilities as
subclassing; however, it can be much more convenient to use and produces smaller
code if there are multiple controls to be altered in the same fashion.

MORE INFORMATION
================

The following file is available for download from the Microsoft Download
Center:

  SuperCls.exe
  (http://download.microsoft.com/download/platformsdk/sample70/3.1/W31/EN-US/SuperCls.exe)

For additional information about how to download Microsoft Support files, click
the article number below to view the article in the Microsoft Knowledge Base:

  Q119591 How to Obtain Microsoft Support Files from Online Services

Microsoft used the most current virus detection software available on the date of
posting to scan this file for viruses. Once posted, the file is housed on secure
servers that prevent any unauthorized changes to the file.

To superclass, create a new class that uses the control window procedure instead
of the default window procedure. This enables the application to process the
appropriate messages and to pass the others along to the default procedure where
the messages will be processed correctly based on the control type.

To implement superclassing, create a window of the type to superclass. Query all
available information about the control and use this information when the new
window is created, substituting the class name and window procedure. When this
window procedure is called, process the desired messages and pass the others to
the standard control procedure (determined in the query phase).

By registering a new class, the application can create superclassed controls
using the application resource (RC) file or CreateWindow() function without any
further work, which can eliminate a number of SetWindowLong() calls if many
controls are to be modified in the same manner.

In the SUPERCLS example, the application creates a new control class called
"SuperEdit", which is identical to a regular edit control but refuses to accept
the "b" character.

Look for the string "SuperEdit" in the .C, .RC, and .DEF files to see the
affected areas of the code.

This example shows superclassed Windows controls. Because the class name has been
changed and the application's instance is used in the class registration, all
controls will be created with this application's DS. This causes no problems for
controls. However, this does not work if an attempt is made to superclass
something other than a control. In that case, it is desirable to use the
application's instance with the class so that it will be destroyed when the
application exits. However, it is necessary to perform some additional work
before the call to CallWindowProc() to set the DS for the subclassed window
procedure. The hInstance passed to CreateWindow() determines which DS the
superclassing procedure uses; to have the superclassed procedure use a different
DS, it is necessary to change the DS value. For more information, see the notes
near the call to CallWindowProc().

Each edit control created using DialogBox(), CreateDialog(), or through an RC
file normally has its own DS. When the application changes the class name, the
code within Windows that handles edit controls is not activated. Instead, the
control uses the application's DS as if it were created using CreateWindow().
This does not cause any difficulties except that when the code for the
superclassed edit control calls LocalAlloc(), it consumes space in the
application's local heap. This should not cause problems in most cases.

Additional query words: sub class subclass control

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Keywords          : kbfile kbsample kb16bitonly kbGrpDSUser kbOSWin310 kbWndw kbWndwClass kbWndwProc kbOSWin300 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310
Version           : WINDOWS:3.0,3.1

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