BUG: Events Fail in ATL Containers when Enum Used as Event Parameter

ID: Q237771

The information in this article applies to:

The Microsoft Active Template Library (ATL) 3.0, included with:
- Microsoft Visual C++, 32-bit Editions, version 6.0

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.

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 kbGrpMFCATL
Version : WINDOWS:3.0
Platform : WINDOWS
Issue type : kbbug