Q160910: PRB: No Text/Caption Properties for Subclassed Combo or List

Article: Q160910
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbole kbActiveX kbComboBox kbCtrl kbListBox kbMFC kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL
Last Modified: 30-JUL-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

When you add a stock Text or Caption property to an MFC ActiveX control that
subclasses a Combo or List Box, it will not serialize properly.

CAUSE
=====

When a container attempts to read the Text or Caption property for an MFC
ActiveX control, the MFC framework calls COleControl::GetText. GetText calls
COleControl::InternalGetText. InternalGetText may attempt to get the Text or
Caption property from the control with the following call:

     if (DefWindowProc(WM_GETTEXT, (WPARAM)_cchUsual,
         (LPARAM)m_strText.GetBufferSetLength(_cchUsual)) >= _cchUsual - 1)

In the case of subclassed Combo or List Box control, this call will always return
an empty buffer.

RESOLUTION
==========

It is debatable whether it makes sense to have a Text or Caption property for a
subclassed Combo or List Box. The native Combo and List Box controls do not
respond to the WM_SETTEXT or WM_GETTEXT messages. Therefore, the problem
described above occurs.

If it makes sense to do this in your application, it is easy to make this work:
When adding the Text or Caption property to the ActiveX control, simply select
the stock property and select Get / Set methods. This will give you the ability
to handle the Text or Caption property as if it were a custom property.

STATUS
======

This behavior is by design.

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

The Text and Caption properties of an ActiveX control are synonymous.

Additional query words:

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Keywords          : kbole kbActiveX kbComboBox kbCtrl kbListBox kbMFC kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:4.0,4.1,4.2,5.0,6.0
Issue type        : kbprb

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