How To VC++ MFC Client for the ComCallingJava Sample

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It is easy to generate a ColeDispatchDriver-derived class in MFC by creating a new class in ClassWizard using the type library created by Visual J++. However, to create the Java object and attach the wrapper, you must first call COleDispatchDriver::CreateDispatch(), then QueryInterface() for the correct dispinterface.

Calling QueryInterface() is necessary because, by default, Java objects use AutoIDispatch as the default dispinterface. CreateDispatch() just calls CoCreateInstance() for IUnknown and then does a QueryInterface() on the IUnknown for IDispatch. AutoIDispatch assigns DISPIDs during run time and can be used only when doing late binding.

It is also possible to have the Java object associate the class as the default dispinterface by implementing an interface called com.ms.com.NoAutoScripting. This interface does not have any methods associated with it, but tells the VM (virtual memory) to not make IDispatch available as the default interface through AutoIDispatch.

Use the following steps to create the client:

1. Follow the steps in the ComCallingJava sample to create a typelib, to create a wrapper class, and to build and register the Java class.
2. Create an AppWizard-generated application, either SDI (single-document interface) or MDI (multiple-document interface).
3. Initialize OLE by calling AfxOleInit() in CWinApp::InitInstance().
4. Create a COleDispatchDriver wrapper for the Euclid Java class using the type library created in step 1. You can do this in ClassWizard by choosing "Add Class..." and then "From a type library...".
5. Using ClassWizard, handle the WM_LBUTTONDOWN message in the CView. Use the following code as a guide for the button handler:

         //(33B0ECE2-E706-11CF-A0C2-00AA00A71DD8)
         static const CLSID GCDclsid =
            { 0x33B0ECE2, 0xE706, 0x11CF, { 0xa0, 0xC2, 0x0, 0xaa, 0x0, 0xa7,
              0x1d, 0xd8 }};
   
         // (33B0ECE1-E706-11cf-A0C2-00AA00A71DD8)
         static const CLSID IGCDclsid =
         { 0x33B0ECE1, 0xE706, 0x11CF, { 0xa0, 0xC2, 0x0, 0xaa, 0x0, 0xa7,
           0x1d, 0xd8 }};
   
         void CComjavaView::OnLButtonDown(UINT nFlags, CPoint point)
         {
            CString str;
            LPDISPATCH pDisp;
   
            IGCD VJCom;
            VJCom.CreateDispatch(GCDclsid);
   
            pDisp = VJCom.m_lpDispatch;
            HRESULT hr = pDisp->QueryInterface( IGCDclsid,
                                                (void**)&VJCom.m_lpDispatch);
            if (hr == S_OK)
               pDisp->Release();
            else
               VJCom.m_lpDispatch = pDisp;
   
            str.Format("The least common denominator of 40 and 24 is %d",
                        VJCom.GCD(40,24));
            AfxMessageBox(str);
            VJCom.ReleaseDispatch();
   
            CView::OnLButtonDown(nFlags, point);
         }
   						

(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Kelly Marie Ward, Microsoft Corporation