COM

BSTR *pBSTR = (BSTR*)CoTaskMemAlloc(sizeof(BSTR));

VariantClear( p );
VariantInit( p );
p->vt = VT_BSTR;
p->pbstrVal = SysAllocString( L"abc" );

STDMETHODIMP CDCSClient::CallService(/*[in,out]*/ VARIANT *p)
{
  if (V_VT(p) == (VT_VARIANT | VT_BYREF))
  {
     // only here you can change the type of passed variable (see VB example below)
     VARIANT *p2 = V_VARIANTREF(p);
     p2->vt = VT_BSTR;
     p2->bstrVal = SysAllocString( L"abc" );
     return S_OK;
  }
}

Dim v As Variant
v = 1
Debug.Print TypeName(v) & " " & v
Call obj.CallService(v)
Debug.Print TypeName(v) & " " & v

p->vt = VT_BSTR | VT_BYREF;
BSTR *pBSTR = new BSTR;
*pBSTR = SysAllocString( L"abc" );
p->pbstrVal = pBSTR;

p->vt = VT_BSTR;
p->bstrVal = SysAllocString( L"abc" );

nicetohaveyou wrote:

IntPtr ProblemCauser = (IntPtr)(-100)

 m_excelAddInUtils = (IAddInUtilities)obj;

// create a Channel with port 0 --> otherwise an Exception will be
//throwed: "This remoting proxy has no channel sink which means either 
//the server has no registered server channels that are listening, or 
//this application has no suitable client channel to talk to the server.
IpcChannel serverChannel = new IpcChannel("localhost:0");
ChannelServices.RegisterChannel(serverChannel);

//Use a second instance of the utility class. With the first instance provided by the COMAddIn.Object property, I 
//haven't found out how to marshal an event registering without throwing 
//an InvalidCastException
AddInFIMUtilities addInUtilClass = new AddInFIMUtilities();

//Register the second instance (CLR object) to the COM instance over the 
//provided utility interface
m_excelAddInUtils.AddToSaveObserverList(addInUtilClass);
//Now the event registering works without cast exceptions
addInUtilClass.AddInSaveEvent += new AddInSaveEventHandler(addInUtilClass_OnFIMSaved);

public delegate void AddInSaveEventHandler();

[Guid("69075652-6A6D-442c-B534-5816D5046F04")]
[ComVisibleAttribute(true)]
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
public interface IAddInEvents
{
    void AddInSaveEventHandler();
}

[Guid("6CA66587-1A1E-4cd6-B55A-20F07F18C343")]
    [ComVisibleAttribute(true)]
    [InterfaceType(ComInterfaceType.InterfaceIsDual)]
    public interface IAddInUtilities
    {
        //Service to register the CLR client object to COM observer list
        [DispId(1)]
        void AddToSaveObserverList(IAddInUtilities addInUtils);

        [DispId(2)]
        void FireSaveEvent();
    }

public void AddToSaveObserverList(IAddInUtilities addInUtils)
{
    Globals.ExcelFIMAddIn.SaveObserverList.Add(addInUtils);
}

public void FireSaveEvent()
{
    AddInSaveEvent();
}

<pre>private List<IAddInUtilities> m_saveObserverList = new List<IAddInUtilities>();

foreach (IAddInUtilities addInFIMUtil in this.SaveObserverList)
{
    try
    {
        ((AddInFIMUtilities)addInUtil).FireSaveEvent();
    }
    catch
    {
                    
    }
}