Q173026: PRB: Message-Handlers for ActiveX Control Aren’t Called

Article: Q173026
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.0a,4.1,4.2,4.2b,5.0,6.0
Operating System(s): 
Keyword(s): kbActiveX kbMFC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL
Last Modified: 02-MAY-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, 4.0a, 4.1, 4.2b 
   - 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 create an ActiveX control dynamically via CWnd::CreateControl(), your
window's message-handlers in the CWnd-derived class will not be called. For
example, if you create a handler for WM_KILLFOCUS [OnKillFocus()] in the
CWnd-derived class of a Microsoft Masked Edit control, it will not be called.

CAUSE
=====

CWnd::CreateControl() doesn't subclass the HWND associated with the control.

RESOLUTION
==========

For message-handlers to be called, the CWnd-derived class needs to subclass the
HWND. You can do this by calling SubclassDlgItem(). Calling SubclassDlgItem()
right after CreateControl() will cause an assert because CreateControl()
previously called CWnd::Attach(). SubclassDlgItem() will call Attach() again. To
avoid this assert, we need to call Detach() first before calling
SubclassDlgItem() as follows:

     // m_MaskEdit is the Microsoft Masked Edit control and 100 is
     // its resource ID.
     m_MaskEdit.Create("", WS_VISIBLE | WS_CHILD | WS_TABSTOP,
        CRect(0,0,100,25), this, 100);
     m_MaskEdit.Detach();
     m_MaskEdit.SubclassDlgItem(100, this);

STATUS
======

This behavior is by design.

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

To set up a message handler for WM_KILLFOCUS in the CWnd-derived class of
Microsoft Masked Edit control, you'll need to add the following lines to the
header file:

     afx_msg void OnKillFocus(CWnd* pNewWnd);
     DECLARE_MESSAGE_MAP()

The following lines go in the .CPP file:

     BEGIN_MESSAGE_MAP(CMSMask, CWnd)
        ON_WM_KILLFOCUS()
     END_MESSAGE_MAP()

     void CMSMask::OnKillFocus(CWnd* pNewWnd)
     {
        TRACE ("CMSMask::OnKillFocus\n");
     }

When you insert an ActiveX control via Component Gallery, the Visual C++ wrapper
class has Create() functions that end up calling CWnd::CreateControl().

Additional query words: ocx

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Keywords          : kbActiveX kbMFC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:4.0,4.0a,4.1,4.2,4.2b,5.0,6.0
Issue type        : kbprb

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