FIX: pvarResult Should Be NULL When vtRet==VT_EMPTY

RESOLUTION

To work around this problem, derive your own class from COleDispatchDriver, such as CMyOleDispatchDriver, and create your own InvokeHelperVoid function. Then call your own InvokeHelperVoid function instead of InvokeHelper when you need to call a method that has no return value.

To implement this work around, create two new functions in your COleDispatchDriver derived class:

   CMyOleDispatchDriver::InvokeHelperVVoid
   CMyOleDispatchDriver::InvokeHelperVoid
				

Implement these functions by copying the implementations of InvokeHelperV and InvokeHelper from OLEDISP2.CPP.

Then modify the following line in InvokeHelperVoid from:

   InvokeHelperV(dwDispID, wFlags, vtRet, pvRet, pbParamInfo,
     argList);
				

   InvokeHelperVVoid(dwDispID, wFlags, vtRet, pvRet, pbParamInfo,
     argList);
				

Then modify the following lines in InvokeHelperVVoid from:

   HRESULT hr = m_lpDispatch->Invoke(dwDispID, IID_NULL, 0, wFlags,
      &dispparams, &vaResult, &excepInfo, &nArgErr);
				

   HRESULT hr = m_lpDispatch->Invoke(dwDispID, IID_NULL, 0, wFlags,
            &dispparams, NULL, &excepInfo, &nArgErr);
				

On some servers, you may also need to re-implement the COleDispatchDriver::SetProperty function and replace it with your own SetPropertyVoid function by copying the implementation from OLEDISP2.CPP. Just as for the InvokeHelper function, you will need to change it to call InvokeHelperVVoid instead of InvokeHelperV.