Re: Default Implementation for IUnknown

"Igor Tandetnik" <>
Tue, 8 May 2007 11:15:16 -0400
Stefan Weber <> wrote:

Now, I'm sticking to yours as well and have the
folloing event sink:

class ATL_NO_VTABLE DOMEventHandler :
public IDispEventImpl<1, DOMEventHandler, &DIID_HTMLElementEvents2,
&LIBID_MSHTML, 1, 1> {

A callback object usable with attachEvent is completely different from
an event sink attached with the connection point. The latter does need
to implement DIID_HTMLElementEvents2 and handle events with various
does not. Its Invoke implementation is only ever called with a DISPID of

Since the callback does not implement any particular named
dispinterface, there is no suitable definition in any available TLB, and
thus IDispEventImpl cannot be used. That's why I use
IDispEventSimpleImpl and manually describe the expected method

I've actually wrote a sample and tested my code. It works for me. The
only change I had to make is to remove IDispatch* parameter (both from
the OnEvent prototype and from EventIno), since you are now using
put_onclick and not attachEvent as you suggested earlier.

This is how I attach the sink:

CComPtr<IHTMLElement> spElem = /* initialized somehow */;
MySink* pSink = new MySink;
IDispatch* pSinkDisp = pSink->GetIDispatch();

This code eventually leaks MySink instance: for the purposes of the
sample, I didn't bother to delete it during shutdown. You may want to be
more careful. Be aware that IDispEvent[Simple]Impl provides a fake
implementation of AddRef and Release that just return without doing
anything. In other words, this sink object is _not_ reference counted,
you must explicitly delete it once you no longer need it. Or,
alternatively, implement AddRef and Release so it deletes itself.
With best wishes,
    Igor Tandetnik

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