PRB: Event Firing Changes in MFC May Break Some Containers

• Microsoft Visual C++, 32-bit Edition, version 4.2

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:

   ARTICLE_ID: Q156934
   TITLE     : PATCH: Visual C++ 4.2b Patch

Keywords          : MfcOLE kb3rdparty
Technology        : kbole kbMfc
Version           : 4.20
Platform          : NT WINDOWS
Issue type        : kbprb