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Win32 COM Collections

Dale Strickland-Clark dale at out-think.NOSPAMco.uk
Wed Aug 16 18:58:27 EDT 2000 
That's very useful. Thanks

--
Dale Strickland-Clark
Out-Think Ltd, UK
Business Technology Consultants

Alex Martelli <alex at magenta.com> wrote in message
news:8nermr0mu0 at news1.newsguy.com...
> "Dale Strickland-Clark" <dale at out-think.NOSPAMco.uk> wrote in message
> news:MGzm5.11088$t45.379508 at news-east.usenetserver.com...
> > (Sorry if this appears twice. It's not showing on my server)
> > I need to pass a collection back via COM and I believe I do this by
> passing
> > back a list of objects? (Please correct me if I'm wrong!)
>
> I think that a list of objects, that you passed back, would be seen
> by the COM server as an array (safearray), not as a collection.
>
> A collection is an object; its defining characteristic is that it
> implements a method (or property) with dispid DISPID_NEWENUM,
> which returns an enumerator (implementation of the interface
> IEnumVariants).
>
> So, basically, you have to implement a COM Server Python
> object, with the appropriate methods, including one called
> _NewEnum which will return the suitable IEnumVariants
> implementation.  The easiest way is to import module
> win32com.server.util and make use of the ListEnumerator
> class it offers -- it implements IEnumVariants on top of
> any Python sequence (a list is OK, but so are tuples, or
> your own sequence-implementing classes).  You can also
> use the ListEnumeratorGateway class if some items on
> the list are not-yet-wrapped Python objects.
>
> Easiest way to access either class, in turn, is through
> the function NewEnum also made available by that same
> util.py module; it returns a properly COM-wrapped
> instance of either class (ListEnumerator by default).
>
> Easiest of all, by using the NewCollection function (still from
> that same module!) you'll return an instance of the Collection
> class (from the same module) which does all of the work
> of a typical Collection object on top of a Python sequence
> object!  You may want to override (and probably call) some
> of its methods if there is something special you want to
> do when items get added/read/deleted/etc, or you may
> get similar effects by passing your own sequence class.
>
>
>
> > How do I implement methods on a collection? For example, to add a new
item
> > to the collection. Typically this would appear to in the client code as:
> >
> > collection.add(args)
>
> Since you're implementing the COM server object that is
> the collection, you'll also implement the Add, Item, Count,
> and whatever other typical collection methods you want.
> Those are in fact rather easy!
>
> But win32com.server.util.Collection already implements
> Item, Count, Add, Remove, Insert, *and* _NewEnum, so
> you may turn out not to have all that much to do!-)
>
> win32com.servers.dictionary is another module you
> may want to study (note the PLURAL servers here): it
> exposes a Python _dictionary_ a la string-indexed
> Collection.  It's rather specialized, but it may be quite
> instructive, I think.
>
>
> Alex
>
>
>
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