ATL COM - EnumWindows callback function not working with IDispatch::Invoke - c++

Question

I am trying to implement a wrapper function for EnumWindows API function to be included in my wrapper dll, so it can be used with many scripting languages.
First of all, I had to test it using VBScript. I implemented a wrapper function and a callback function for EnumWindows with the help of my useful researches, but it is not working as I want.
Here is the code I currently have:
Wrapper functions for EnumWindows and EnumWindowsProc callback:
BOOL CALLBACK EnumWindowsProc(__in HWND hWnd, __in LPARAM lParam) {
LPENUMWINDOWSPARAMS pewParams;
VARIANT vhWnd, vResult; HRESULT HR = S_OK;
VariantInit(&vhWnd);
VariantInit(&vResult);
vhWnd.vt = VT_I4;
vhWnd.lVal = (LONG)(LONG_PTR)hWnd;
pewParams = reinterpret_cast<LPENUMWINDOWSPARAMS>(lParam);
// ^ PASSING MY PARAMETERS THROUGH LPARAM
CComVariant varArgs[2] = { &vResult, &vhWnd };
DISPPARAMS Parameters = { &varArgs[0], NULL, 2, 0 };
pewParams->DISPATCH->Invoke(0, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD, &Parameters, &vResult, NULL, NULL);
// ^ I SUSPECT SOMETHING IS WRONG WITH THIS INVOKE METHOD. BUT IT RETURNS S_OK.
if (vResult.vt != VT_BOOL) { HR = DISP_E_TYPEMISMATCH; }
pewParams->CallbackResult.vt = VT_ERROR;
pewParams->CallbackResult.scode = HR;
if (HR == S_OK)
return (vResult.boolVal == VARIANT_TRUE ? TRUE : FALSE);
else
return FALSE;
}
STDMETHODIMP CWinAPI::WinAPI_EnumWindows(VARIANT EnumFunc, int lParam, int *Result) {
ENUMWINDOWSPARAMS ewParams; HRESULT HR = S_OK;
switch (EnumFunc.vt)
{
case VT_DISPATCH:
ewParams.DISPATCH = EnumFunc.pdispVal;
break;
case VT_VARIANT | VT_BYREF:
if (EnumFunc.pvarVal->vt == VT_DISPATCH) { ewParams.DISPATCH = EnumFunc.pvarVal->pdispVal; }
break;
default: return DISP_E_TYPEMISMATCH;
}
ewParams.lParam = reinterpret_cast<LPVARIANT>(&lParam);
*Result = (int)EnumWindows(EnumWindowsProc, reinterpret_cast<LPARAM>(&ewParams));
HR = ewParams.CallbackResult.scode;
return HR;
}
ENUMWINDOWSPARAMS structure:
typedef struct tagENUMWINDOWSPARAMS {
LPDISPATCH DISPATCH;
LPVARIANT lParam;
VARIANT CallbackResult;
} ENUMWINDOWSPARAMS, *PENUMWINDOWSPARAMS, *LPENUMWINDOWSPARAMS;
Here is the testing VBScript I am currently using:
Dim WINAPI: Set WINAPI = WScript.CreateObject("WinAPIWrapperLib.WINAPI")
Function EnumWindowsProc(HWND, lParam)
WScript.Echo "Handle to the window: 0x" + CStr(UCase(Hex(HWND)))
EnumWindowsProc = True
End Function
Dim Result: Result = WINAPI.WinAPI_EnumWindows(GetRef("EnumWindowsProc"), 0)
WScript.Echo "EnumWindows returned " + CStr(Result)
One thing works, EnumWindows is returning True.
But, instead what I expect, I am not getting handles of windows echoed.
And when I call GetLastError, it returns ERROR_SUCCESS.
Thanks in advance for your kind help.

Answer 1

I fixed the problem, nothing special done, it's only a small change:
Changed varArgs's type from CComVariant to VARIANT like this:
VARIANT varArgs[2] = { vResult, vhWnd };
Changed DISPPARAMS as below:
DISPPARAMS Parameters = {};
Parameters.cArgs = 2;
Parameters.rgvarg = varArgs;
Invoke method is still the same:
pewParams->DISPATCH->Invoke(0, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD, &Parameters, &vResult, NULL, NULL);
Any good suggestions are further appreciated.