PRB: GetControlUnknown() Returns NULL in COleControl

 Last reviewed: August 7, 1997
Article ID: Q166767
The information in this article applies to:
  • Microsoft Visual C++, 32-bit Editions, versions 4.2, 4.2b, 5.0

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. 

Keywords          : MfcOLE kbprg
Technology        : kbole
Version           : 4.2 4.2b 5.0
Platform          : NT WINDOWS
Issue type        : kbprb

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Last reviewed: August 7, 1997
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