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Q192347: PRB: Focus/Activation Problems with MFC Control on VB Forms

Article: Q192347
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:5.0,6.0; winnt:5.0,6.0
Operating System(s): 
Keyword(s): kbcode kbActiveX kbMFC kbVBp500 kbVBp600 kbVC500 kbVC600 kbGrpDSVB
Last Modified: 07-MAY-2001

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The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

You have an ActiveX control created in Visual C++ using the Microsoft Foundation
Classes (MFC). When two of these controls reside on different Visual Basic MDI
child forms, and you attempt to switch from one form to another by clicking on
the controls, focus shifts to the control, but the expected Activate/Deactivate
form events do not occur. Code in the events does not run, and the Active Title
Bar does not switch as expected. Under Windows 2000, the Activate/Deativate form
events do fire as expected, but the Active Title Bar still does not switch as
expected.

CAUSE
=====

Windows MDI child activation is based on the MDI client window getting the
WM_PARENTNOTIFY message. A control created in MFC has a window style of
WS_EX_NOPARENTNOTIFY by default. This suppresses the parent notification
message, causing the problem described above.

RESOLUTION
==========

To resolve this problem, change the window style of the control. There are two
ways to accomplish this. Resolution #1 requires alteration of the control's
source code. It is the recommended solution, but does require source code
access. Resolution #2 presents a way to resolve this situation in the Visual
Basic client application. Resolution #2 has one requirement: The control must
expose an hWnd property.

NOTE: The hWnd property is a stock property of an MFC control, but by default it
is private to the control.

If you do not have access to the control's source code, and the hWnd property has
not been exposed, then neither of these solutions works.

Resolution #1
-------------

Change the window style of the control in PreCreateWindow. This example uses a
hypothetical control named CPushCtrl, derived from the button class.

Sample Code
-----------

     BOOL CPushCtrl::PreCreateWindow(CREATESTRUCT& cs)
     {
       cs.lpszClass = _T("BUTTON");
       cs.style |= BS_PUSHBUTTON | BS_OWNERDRAW;

        // The next statement allows the Visual Basic Child forms to get
        // focus correctly.
       if (cs.dwExStyle & WS_EX_NOPARENTNOTIFY)
          cs.dwExStyle -= WS_EX_NOPARENTNOTIFY;

       return COleControl::PreCreateWindow(cs);
     }

Resolution #2
-------------

If it is not possible to change the code for the control, you can use the Win32
API from the Visual Basic client to change this value.

1. Add the following code to a BAS module, and add the module to any project
  that uses the ActiveX control:

        Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _
         (ByVal hwnd As Long, ByVal nIndex As Long, _
           ByVal dwNewLong As Long) As Long
        Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" _
         (ByVal hwnd As Long, ByVal nIndex As Long) As Long

        Public Sub fixWindowStyle(handle As Long)
           Dim ret As Long
           Dim b As Boolean
           ret = GetWindowLong(handle, -20)
           ret = ret - 4
           b = SetWindowLong(handle, -20, ret)
        End Sub

2. Add the following code to the Load Event for any form hosting the ActiveX
  control. (The control name is Push1 in this example):

        fixWindowStyle (Push1.hwnd)

STATUS
======

This behavior is by design.

Additional query words:

======================================================================
Keywords          : kbcode kbActiveX kbMFC kbVBp500 kbVBp600 kbVC500 kbVC600 kbGrpDSVB 
Technology        : kbVCsearch kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVB500 kbVB600 kbVC500 kbVC600 kbVC32bitSearch kbVC500Search
Version           : WINDOWS:5.0,6.0; winnt:5.0,6.0
Issue type        : kbprb

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