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

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This article was previously published under Q237771

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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.

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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.

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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:

194179 (http://support.microsoft.com/kb/194179/ ) AtlEvnt.exe sample shows how to create ATL sinks by using the ATL IDispEventImpl and IDispEventSimpleImpl classes

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;
}

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STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section. This problem was corrected in Microsoft Visual C++ .NET.

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REFERENCES

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

194179 (http://support.microsoft.com/kb/194179/ ) AtlEvnt.exe sample shows how to creates ATL sinks by using the ATL IDispEventImpl and IDispEventSimpleImpl classes

181277 (http://support.microsoft.com/kb/181277/ ) The AtlSink.exe sample demonstrates how to implement a dispinterface sink by using the Active Template Library (ATL) in Visual C++

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

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