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Q80822: NoSwitch.exe Prevents Windows from Switching Tasks

Article: Q80822
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 kbOSWin300
Last Modified: 10-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
=======

NoSwitch.exe is a sample application that demonstrates how an application can
disable the task switch. Certain types of applications, such as security
applications and possibly some setup programs, require the ability to disable
task switching under Windows. To disable task switching, the program must
prevent the user from accessing the Task List, using mouse or keystroke
combinations to switch to other applications, and so forth.

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

The following files are available for download from the Microsoft Download
Center:

NoSwitch.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.


NOSWITCH demonstrates how an application can disable task switching. The
application must take the following four steps to disable task switching:

1. Subclass the desktop window to prevent the Task List from being displayed
  when the user double-clicks the desktop window.

2. Prevent the user from using key combinations to switch to another task by
  trapping the following three wParam values for the WM_SYSCOMMAND message:
  SC_NEXTWINDOW, SC_PREVWINDOW, and SC_TASKLIST.

3. Prevent other applications from activating themselves by enumerating all
  top-level windows, and disabling the windows that do not belong to this
  application.

4. Each time a WM_INITMEMUPOPUP message is received for the system menu, disable
  the menu items that relate to switching tasks.

Before exiting the application, reverse the effects of any actions taken to
prevent switching tasks. Refer to the NOSWITCH sample for complete details.

There is a simpler, more limited, method to disable task switching. If the
application is run as a maximized window, then step 2 above is enough to prevent
switching tasks. However, the application must prevent the window from being
restored or minimized. The limitation to this method is that the application
must run as a maximized window.

Additional query words:

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

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