| Re: passing parameters from base to base [message #33032 is a reply to message #33004] |
Wed, 27 November 2002 16:14   |
JD Smith
Messages: 850
Registered: December 1999
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Senior Member |
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On Tue, 26 Nov 2002 11:47:37 -0700, Pavel A. Romashkin wrote:
> This sounds sensible, although I didn't see one piece of information (or
> did I miss it?) - how do ObjMsg objects know about each other? There has
> to be a place they go to when they want to "sign up". Is the awareness
> established at initialization, or in a common block? How do they become
> aware of each other?
> Cheers,
> Pavel
>
You put your finger right on the tricky bit (good eye ;). Right now,
my solution is to "introduce" objects which want to communicate to
each other on a higher level. E.g. I might say in my wrapper program:
oDraw=obj_new('tvDraw')
oFunk=obj_new('tvFunky',oDraw)
oNother=obj_new('tvNother',oDraw)
and oFunk could sign up for the tvDraw messages it needs. Perhaps
oFunk even builds an ObjMsg object of its own and signs up with it
directly. Usually this is perfectly adequate: relations and
introductions can be done at compile time or Init time. This works
well for, e.g., building a viewer shell with all the desired plug-ins,
especially when you need to carry widget bases around to build the
interface inside.
But sometimes you'd like to find new ObjMsg objects to communicate
with at run time (maybe because they didn't exist yet when you were
first made). For this I use one other mechanism: if you have an
ObjMsg object, you can query for other ObjMsg objects on *its* message
recipient list, typically by class name (sort of a "friend of a
friend" thing). E.g., if I knew that my oDraw object probably had
relations with an object of class 'tvColor' that I needed to talk to,
I'd say:
oColor=self.oDraw->GetMsgObjs(CLASS='tvColor')
I'd probably make it robust in case there's no such object to
communicate with. Objects which have an absolute dependency on each
other to function should probably introduce themselves the "old
fashioned way".
Any suggestions much appreciated. Another option is to publish
"capabilities" or lists of potential messages sent in a common block
of some kind, but that gets complicated with many multiples of the
same type of object on the global stack.
JD
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