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Q157970: PRB: Event Firing Changes in MFC May Break Some Containers

Article: Q157970
Product(s): Microsoft C Compiler
Version(s): winnt:4.2
Operating System(s): 
Keyword(s): kb3rdparty kbActivexEvents kbContainer kbCtrl kbMFC kbVC420 kbfix kbGrpDSMFCATL
Last Modified: 04-AUG-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
- Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
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SYMPTOMS
========

ActiveX Control containers implemented with Borland Delphi (and possibly other
containers as well) may not see events fired by ActiveX Controls created with
MFC version 4.2. The same container may have been able to handle events fired by
a version of the same control created with MFC 4.1 or earlier.

CAUSE
=====

The problem is related to a change made in MFC 4.2's implementation of the
IConnectionPoint::Advise method. In MFC 4.1, the framework does a QueryInterface
on the passed in IUnknown specifying the GUID of the default event set of the
control.

In MFC 4.2, the framework was changed to do a QueryInterface on the passed in
IUnknown for IDispatch. Failing that, it queries for the event set interface.

The change made to MFC 4.2 may make some containers unable to handle the events
fired by the control. The problem is usually related to the way the container
has implemented its control container support.

RESOLUTION
==========

This problem has been addressed with the Visual C++ 4.2 patch. With this patch,
MFC's implementation of IConnectionPoint::Advise has been changed back to doing
an initial QueryInterface on the passed in IUnknown specifying the GUID of the
default event set of the control. Failing that, it queries for IDispatch.

STATUS
======

This behavior is by design.

REFERENCES
==========

For information on how to obtain the Visual C++ 4.2 patch, please see the
following article in the Microsoft Knowledge Base:

  Q156934 PATCH: Visual C++ 4.2b Patch

Additional query words:

======================================================================
Keywords          : kb3rdparty kbActivexEvents kbContainer kbCtrl kbMFC kbVC420 kbfix kbGrpDSMFCATL 
Technology        : kbVCsearch kbAudDeveloper kbVC420 kbVC32bitSearch
Version           : winnt:4.2
Issue type        : kbprb

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