BUG: "0x80070057 (E_INVALIDARG - The parameter is incorrect)" error message when you use an ATL to catch an event when an enum is used as a parameter of the event (237771)

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 more information about SINK_ENTRY_INFO, click the following article number to view the article in the Microsoft Knowledge Base: 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;
}