KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q247797: Extra LBN_SELCHANGE Notification for Drop-Down List Boxes

Article: Q247797
Product(s): Microsoft Windows NT
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): kbWinNT400PreSP7Fix
Last Modified: 08-MAY-2002

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows NT Server version 4.0 
- Microsoft Windows NT Workstation version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Windows NT 4.0 generates an LBN_SELCHANGE notification for drop-down list boxes
in the following circumstances:

1. The user clicks the arrow on the right side of the drop-down list box to drop
  the list down.

2. The user moves the mouse pointer down the list causing various items in the
  list to be selected, but does not click any item.

3. The user moves the mouse pointer outside the list box, and then clicks the
  mouse to close the drop-down list.

At this point, a sequence of windows messages are sent to the program. Under
Windows NT 4.0, this includes an extraneous LBN_SELCHANGE notification for the
list box. It is incorrect to send an LBN_SELCHANGE notification at this point
because clicking outside of a dropped-down list box to close it as described
above does not change the current selection in the list box.

Microsoft Visual Basic programs may see this as an extra Click event if a Click
method is defined for the list box.

Some programs that run without problems under Windows NT 3.51 may malfunction
when they receive this unexpected notification under Windows NT 4.0.

RESOLUTION
==========

A supported fix is now available from Microsoft, but it is only intended to
correct the problem described in this article and should be applied only to
systems experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the
fix. For a complete list of Microsoft Product Support Services phone numbers and
information on support costs, please go to the following address on the World
Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are normally incurred for support calls may
be canceled, if a Microsoft Support Professional determines that a specific
update will resolve your problem. Normal support costs will apply to additional
support questions and issues that do not qualify for the specific update in
question.

The English version of this fix should have the following file attributes or
later:

  Date      Time                 Size    File name     Platform
  -------------------------------------------------------------
  10/12/99  00:58                326,416 User32.dll    Intel
  10/12/99  00:57                577,296 User32.dll    Alpha



WORKAROUND
==========

Recode the program to handle the extra notification gracefully.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products that are
listed at the beginning of this article.

Additional query words:

======================================================================
Keywords          : kbWinNT400PreSP7Fix 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : winnt:4.0
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.