Re: Diff between interface, IDispatch interface and dispinterface

From:
"Igor Tandetnik" <itandetnik@mvps.org>
Newsgroups:
microsoft.public.vc.atl
Date:
Mon, 8 May 2006 08:11:57 -0400
Message-ID:
<#a#8XipcGHA.3908@TK2MSFTNGP02.phx.gbl>
"Egbert Nierop (MVP for IIS)" <egbert_nierop@nospam.invalid> wrote in
message news:uX33QZncGHA.5116@TK2MSFTNGP02.phx.gbl

From what I understand and from experience, you cannot QI
(queryinterface) on dispinterface


Actually, you normally can. A dispinterface usually has its own IID,
sometimes referred to as DIID (dispinterface IID). What you get back
from QI is an IDispatch pointer, of couse.

For example, an event sink (typically a dispinterface) is required to
respond positively to QI for an IID of a source interface it's
implementing. Most IConnectionPoint implementations will return
CONNECT_E_CANNOTCONNECT from Advise if given an interface that fails
this QI call.

IDispatch is meant to be Dual.


Dual interfaces are actually a fairly late invention in COM history.
IDispatch predates them.
--
With best wishes,
    Igor Tandetnik

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