Q237771: FIX: Events Fail in ATL Containers if Enum Used as Parameter

Article: Q237771
Product(s): Microsoft C Compiler
Version(s): 3.0,6.0
Operating System(s): 
Keyword(s): kbActivexEvents kbAutomation kbCOMt kbConnPts kbVC600bug kbATL300bug kbDSupport kbGrpDS
Last Modified: 10-FEB-2002

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The information in this article applies to:

- The Microsoft Active Template Library (ATL) 3.0, used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

An ATL event sink defined with SINK_ENTRY or SINK_ENTRY_EX will fail to catch an
event when an enum is used as one of the parameters for the event. The failure
code returned by IDispatch::Invoke is "0x80070057 (E_INVALIDARG - The parameter
is incorrect)." The event will succeed in another container, such as Visual
Basic.

CAUSE
=====

IDispEventImpl's GetFuncInfoFromID method checks the type of the event
parameters and, on encountering type VT_USERDEFINED, calls GetUserDefinedType.
This method currently checks only for TKIND_ALIAS ("typedef struct" data types)
and not TKIND_ENUM.

RESOLUTION
==========

There are several ways to work around this problem. One method is to use the
SINK_ENTRY_INFO macro and define an _ATL_FUNC_INFO structure to provide type
information for the event method. Use a VT_I4 type for the enum parameter. For
an example, and for more information on SINK_ENTRY_INFO, see the following
article in the Microsoft Knowledge Base:

  Q194179 SAMPLE: AtlEvnt.exe Creates ATL Sinks Using IDispEventImpl

If you are using IDispEventImpl<> for the sink, you can override the
virtual function GetFuncInfoFromID. A simple override is as follows:

  HRESULT GetFuncInfoFromId(const IID& iid, DISPID dispidMember,LCID lcid, _ATL_FUNC_INFO& info)
  {
  	// class base class implementation
      HRESULT hr = IDispEventImpl<IDC_OBJ, CSinkObj, &DIID__IEnumEventEvents, &LIBID_TESTUNKARTICLELib, 1, 0>::GetFuncInfoFromId(iid, dispidMember,lcid, info);
      if (SUCCEEDED(hr))
  	{
          // is this the correct event interface
          if (InlineIsEqualGUID(iid, DIID__IEnumEventEvents))
  		{
              //check for dispid of event with enum param
              switch(dispidMember)
  			{
                  case 1:
                      // the enumeration parameter is change to VT_I4
                      // info.pVarTypes represents the type of params
                      // params are stored in reverse order, with 0 base index
                      if (info.pVarTypes[0] == VT_USERDEFINED)
                          info.pVarTypes[0] = VT_I4;  
                      break;
  			}
  		}
  	}
      return hr;
  }

The most direct approach when using IDispEventImpl<>is to change the
implementation of GetUserDefinedType in Atlcom.h. At line 3968, after the code
block that begins "if(pta && pta->typekind == TKIND_ALIAS)", a second
if statement could be inserted that would set the correct VARTYPE for
enumerations. This block could be written as follows:

  if (pta && pta->typekind == TKIND_ENUM)
  {
      vt = VT_I4;
  }

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

This problem was corrected in Microsoft Visual C++ .NET.

REFERENCES
==========

For additional information, click the article numbers below to view the articles
in the Microsoft Knowledge Base:

  Q194179 SAMPLE: AtlEvnt.exe Creates ATL Sinks Using IDispEventImpl

  Q181277 SAMPLE: AtlSink Uses ATL to Create a Dispinterface Sink

See also the ATL Articles in the Visual C++ documentation, specifically "ATL
Collections and Enumerators" and "Event Handling in ATL."

Additional query words:

======================================================================
Keywords          : kbActivexEvents kbAutomation kbCOMt kbConnPts kbVC600bug kbATL300bug kbDSupport kbGrpDSMFCATL 
Technology        : kbVCsearch kbAudDeveloper kbATLsearch
Version           : :3.0,6.0
Issue type        : kbbug
Solution Type     : kbfix

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