ATL-Implemented Sink Interface

Environment: VC++ 6.0


From my experimence, it’s always a pain to implement sink interface with
MFC wizard. But ATL is much more straightforward and easy to do the
same job. Thanks to the new VC++ 6.0 wizard, we can add ATL to MFC
project now. So we can implement the sink interface using ATL way.
I would like to share my experimence a little tricky thing I figure out with you.
Don’t use the wizard class wrapper generated class, bypassing it and hook
up with server by yourself, you can pass a HDC, HWND or other window
handle to the ATL server. If you used MFC wizard class wrapper, normally
it gernerates an error message in its automatically generated header file:
not emitted because of invalid return type or parameter type.

Here are my procedures:

  1. Create a ActiveX with ATL(Clicker) which expose the connection interface
    _IClickItEvents and three event functions: OnCtrlMouseMove(long x, long y),
    OnCtrlMouseClick(long x, long y), OnCtrlError(BSTR errorMsg).
    An incoming interface was created as well. Which expose functions: SetMode(int 0),
    PaintOverlay(HDC* pHDC).

  2. Create a MFC dialog based application(ClickerClient) project. Right click the
    project name in the class view window and choose “new ATL object”, then
    choose “Add ATL support”. There will be an error message box show up, just
    ignore it. Draw an Clicker activeX on the dialog in the resource file.

  3. Include the Clicker.h and Clicker_i.c to you dialog cpp file. Don’t use the Wizard
    generated class CClickIt, use following code find the IUnknow and IClicker of your
    ActiveX instance:

    IClickIt*   spclicker;
    IUnknown*  pUnk = GetDlgItem(IDC_CLICKIT)->GetControlUnknown();
    pUnk->QueryInterface(IID_IClickIt, (void**) &spclicker));
  4. Create a ATL message event handler class like you did in the ATL client project.

  5. Create an instance of message event handler in the InitDialog() and Advise the
    server connection point there.

  6. Unadvise the server connection point and delete the message handler object in
    the DestroyWindow().

  7. Try pass a HDC to the server interface function PaintOverlay(HDC* pHDC). Server
    will paint a rectangle on you DC.

Demo Information

Download the and
The demo server code will generate an ActiveX clicker.dll, you need to register it before
you play with it.The demo client code will generate a dialog application which showing the
mouse position in the control, mouse click position in the control, also paint the dialog by
calling to the server PaintOverlay(HDC* pHDC) function.


Download client & server demo project – 80 Kb

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