Re: About MIDL and IDispatch

"Igor Tandetnik" <>
Wed, 22 Oct 2008 22:44:46 -0400
<susan> wrote in message

we can declare IDispatch in many way:

// dispinterface DFoo
// {
// properties:
// ...
// methods:
// ...
// }

Properties and methods here are not "real" COM methods. They are simply
agreements on which DISPID and which parameters to pass to
IDispatch::Invoke. An object implementing this interface only needs to
implement seven IDispatch methods.

// [oleautomation]
// interface IFoo : IUnknown
// {
// ...
// }

This has nothing to do with IDispatch at all.

// [dual]
// interface IFoo : IDispatch
// {
// ...
// }

This is a dual interface - an interface derived from IDispatch. It has
seven IDispatch methods, plus a a set of methods specific to IFoo.
Usually (but not always), an object implementing such an interface
implements IDispatch::Invoke by simply forwarding to an appropriate IFoo
method (the DISPID passed to Invoke determines which one).
With best wishes,
    Igor Tandetnik

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