Q166767: PRB: GetControlUnknown() Returns NULL in COleControl

Article: Q166767
Product(s): Microsoft C Compiler
Version(s): winnt:4.2,4.2b,5.0,6.0
Operating System(s): 
Keyword(s): kbole kbActiveX kbCOMt kbCtrl kbInprocSvr kbMFC kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL
Last Modified: 04-AUG-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 4.2b, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 4.2b, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

When you call GetControlUnknown() from inside a COleControl-derived class, it
always returns NULL.

CAUSE
=====

The function CWnd::GetControlUnknown() should be called from the control
container.

RESOLUTION
==========

Call CCmdTarget::GetControllingUnknown() instead of
CWnd::GetControlUnknown().

STATUS
======

This behavior is by design.

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

CWnd::GetControlUnknown() can be called to check if the CWnd is being used as a
proxy, or wrapper, for a contained Activex control. It does this by checking the
m_pCtrlSite CWnd member to see if it's NULL or not. If m_pCtrlSite is NULL, then
NULL is returned. Since m_pCtrlSite is only set when the CWnd represents a
contained ActiveX control, m_pCtrlSite will always be NULL if
GetControlUnknown() is called from inside an ActiveX control's source.

CCmdTarget::GetControllingUnknown() can be used to get the IUnknown of the outer,
or controlling, object from within an object which is being aggregated. If the
object is not being aggregated then CCmdTarget::GetControllingUnknown() simply
returns the object's own IUnknown.

Note that CCmdTarget::GetControllingUnknown() is an undocumented function and may
change in future versions of MFC.

Additional query words:

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Keywords          : kbole kbActiveX kbCOMt kbCtrl kbInprocSvr kbMFC kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL 
Technology        : kbVCsearch kbAudDeveloper kbVC420 kbVC500 kbVC600 kbVC32bitSearch kbVC420b kbVC500Search
Version           : winnt:4.2,4.2b,5.0,6.0
Issue type        : kbprb

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