From: Charles Gamble (Charles.GambleSINGULARITY.CO.UK)
Date: Tue Oct 26 2004 - 11:25:07 CDT

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Hi,

I want to create a simple callback method called by a COM+ DLL server.
The method will be on an object implemented by a C++ client.
I have managed to get it to work for an in-process COM DLL, but as soon as I
put the server object into COM+, I am getting E_NOINTERFACE when doing a
QueryInterface.
I think it is because I have created an internal object in the C++ client.

I have done the following:
1. Added the below interface definition to COM+ DLL IDL:
[
  object,
  //use guidgen to generate a unique id
  uuid(43FF9A45-33E4-4c56-BFE0-CDAEF5058F36),
  dual,
  helpstring("IClientCallback Interface"),
  pointer_default(unique)
 ]

 interface IClientCallback :IDispatch
 {
 [id(1), helpstring("method TestMethod")]
  HRESULT TestMethod();
 };

2. Created a C++ class that implements the interface in the C++ client:
class CClientCallback :
 public CComObjectRootEx<CComSingleThreadModel>,
 public IDispatchImpl<IClientCallback, &IID_IClientCallback,
&LIBID_AWSERVERLib>
{
 public:
  CClientCallback();

BEGIN_COM_MAP(CClientCallback)
 COM_INTERFACE_ENTRY(IClientCallback)
 COM_INTERFACE_ENTRY(IDispatch)
END_COM_MAP()

 STDMETHOD(TestMethod)();
.......

3. I pass in the object to the server object method as follows (as a VARIANT
[in])
CComObject<CClientCallback>* pClientCallback = NULL;
  hr = CComObject<CClientCallback>::CreateInstance(&pClientCallback);
  CHECKHR(hr)

  VARIANT vClientCallback;
  V_VT(&vClientCallback) = VT_DISPATCH;
  V_DISPATCH(&vClientCallback) = (IDispatch*)pClientCallback;

4. Then I query for the interface on the server:
CComPtr<IClientCallback> pClientCallback = NULL;
 hr = V_DISPATCH(&i_vClientCallback)->QueryInterface(IID_IClientCallback,
             (void **)&pClientCallback) ;
 CHECKHR(hr)

 hr = pClientCallback->TestMethod();
 CHECKHR(hr)

The query interface is failing as I've already described. What would I need
to do to make this work?

Thanks,
    Charles Gamble.

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