HOWTO: Create a Sink Interface in MFC-Based COM Client

• Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 4.1, 4.2, 5.0
• The Microsoft Foundation Classes (MFC)

SUMMARY

Microsoft Foundation Classes (MFC) has wizard support to add sink interfaces for ActiveX controls. However, this support does not extend to other COM servers. This article describes how to add a sink interface in an MFC client for source interfaces described by COM servers. Please note that this article applies to source interfaces, which are dispinterfaces, or dual interfaces with events being called through IDispatch::Invoke().

MORE INFORMATION

Here are the steps to add a sink interface to a COM client:

1. Using the Class Wizard, add a CCmdTarget derived object (for example, CMySink) with automation support. In the Class Wizard, select the Automation option rather than "Createable by type ID" option when adding this class.

2. In the interface map, change the IID (the second parameter in the INTERFACE_MAP macro) so that it is the IID of the source interface (usually the interface with the default and/or source attribute in the server's .idl file). The .idl file can be seen by viewing the typelib in the OLE/COM Object Viewer.

3. In the DISPATCH_MAP of CMySink class, add a DISP_FUNCTION_ID macro for each of the events defined in the source interface that you want to handle. For example:

         BEGIN_DISPATCH_MAP(CMySink, CCmdTarget)
           DISP_FUNCTION_ID(CMySink,"Quit",2,OnObjQuit,VT_EMPTY,VTS_I4 VTS_I4)
         END_DISPATCH_MAP()
   
      The code above is an entry for handling the Quit event with a DISPID 2,
      which takes two long parameters and returns a void. OnObjectQuit is a
      CMySink member function that takes two longs and returns a void. This
      function must be added manually and is called when the COM server fires
      a Quit event.
   
   

4. Now you have hooked up the sink interface with the server so that you can start receiving events. To do this, call the AfxConnectionAdvise() function once the server object is created. For example:

         //Instantiate the sink class and hold a pointer to it.
         m_pSink = new CMySink();
   

         //Get a pointer to sinks IUnknown, no AddRef. CMySink implements only
         //dispinterface and the IUnknown and IDispatch pointers will be same.
         LPUNKNOWN pUnkSink = m_pSink->GetIDispatch(FALSE);
   

         //Establish a connection between source and sink.
         //m_pUnkSrc is IUnknown of server obtained by CoCreateInstance().
         //m_dwCookie is a cookie identifying the connection, and is needed
         //to terminate the connection.
         AfxConnectionAdvise(m_pUnkSrc, IID_MYEVENT, pUnkSink, FALSE,
            &m_dwCookie);
   
   

5. When you have finished using the server object you need to terminate the connection before releasing the server object. You do this by calling the AfxConnectionUnadvise() function. For example:

         //Get a pointer to sinks IUnknown, no AddRef.
         LPUNKNOWN pUnkSink = m_pSink->GetIDispatch(FALSE);
   

         //Terminate a connection between source and sink.
         //m_pUnkSrc is IUnknown of server obtained by CoCreateInstance().
         //m_dwCookie is a value obtained through AfxConnectionAdvise().
         AfxConnectionUnadvise(m_pUnkSrc, IID_MYEVENT, pUnkSink, FASLE,
            m_dwCookie);
   
   

REFERENCES

The sink component of the Connpts.exe sample illustrates implementation of the sink interface.

For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q152087
   TITLE     : SAMPLE: Connpts.exe Implements Connection Points in MFC Apps

Keywords          : MfcOLE
Version           : WINNT:2.0,2.1,2.2,4.0,4.1,4.2,5.0
Platform          : winnt
Issue type        : kbhowto