PRB: Dispatch Interface for Automation Object Must Be Registered

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Visual Basic does typesafe binding to an automation object when a variable is dimensioned as a specific type. For instance: When developing this code, establish a reference to the TestVB module (in the Visual Basic development environment, select Tools, References, and Browse for the TestVB type library). Select the type library to register the type library and the dispatch interface for the Document object.

The problem occurs when the Visual Basic program and the automation server are loaded on a machine other than the development machine. Even if the automation server is initially run to perform self-registration, the dispatch interface for the automation object will not be registered and the "New" syntax will fail to create the automation object.

To eliminate this problem, it is necessary to register the dispatch interface for the automation object on the non-development machine. This can be done programmatically or with a .reg file during setup.

In the case of the TestVB module, the Document object's dispatch interface is the ITestVB interface, which is defined as follows in the .cpp file for the Document object:

   // Note: We add support for IID_ITestVB to support typesafe binding
   // from VBA. This IID must match the GUID that is attached to the
   // dispinterface in the .ODL file.

   // {1249A4D2-D469-11CF-A68F-00AA00A70FC2}
   static const IID IID_ITestVB =
   { 0x1249a4d2, 0xd469, 0x11cf,
           { 0xa6, 0x8f, 0x0, 0xaa, 0x0, 0xa7, 0xf, 0xc2 } };

   BEGIN_INTERFACE_MAP(CTestVBDoc, CDocument)
       INTERFACE_PART(CTestVBDoc, IID_ITestVB, Dispatch)
   END_INTERFACE_MAP()
				

The following .reg file will register the ITestVB interface and enable marshaling of the interface via the standard IDispatch proxy and stub.

   REGEDIT
   
   HKEY_CLASSES_ROOT\Interface\{1249A4D2-D469-11CF-A68F-00AA00A70FC2}
           = ITestVB
   HKEY_CLASSES_ROOT\Interface\{1249A4D2-D469-11CF-A68F-00AA00A70FC2}
           ProxyStubClsid = {00020420-0000-0000-C000-000000000046}
   HKEY_CLASSES_ROOT\Interface\{1249A4D2-D469-11CF-A68F-00AA00A70FC2}
           ProxyStubClsid32 = {00020420-0000-0000-C000-000000000046}
				

To programmatically register the interface, #include <winreg.h>, and insert the following code (with the proper dispatch ID) in the InitInstance of the automation server:

   HKEY key;

   // Open HKEY_CLASSES_ROOT
   RegOpenKey(HKEY_CLASSES_ROOT, _T("Interface"), &key);

   // Set up the key
   RegSetValue( key,
       _T("{1249A4D2-D469-11CF-A68F-00AA00A70FC2}"), REG_SZ,
       _T("ITestVB"), 0);
   RegSetValue( key,
       _T("{1249A4D2-D469-11CF-A68F-00AA00A70FC2}\\ProxyStubClsid"),
       REG_SZ, _T("{00020420-0000-0000-C000-000000000046}"), 0);
   RegSetValue( key,
       _T("{1249A4D2-D469-11CF-A68F-00AA00A70FC2}\\ProxyStubClsid32"),
       REG_SZ, _T("{00020420-0000-0000-C000-000000000046}"), 0);

   RegCloseKey(key);