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Re: [Gnumed-devel] inter-module communication

From: Hilmar Berger
Subject: Re: [Gnumed-devel] inter-module communication
Date: Tue, 3 Sep 2002 00:05:43 +0200 (CEST)


On Mon, 2 Sep 2002, Horst Herb wrote:

> 1.) any widget interested in particular data should register it's interest 
> via 
> gmDispatcher.
> Example: A "person info" widget displaying name & address of the currently 
> active patient needs to know when the patient has been changed.
> Thus, it registers it's own callback function (which subsequently updates the 
> widget) with gmDispatcher.
> Any widget that changes the current patient, will must notify gmDispatcher, 
> who in turn will fire all the registered callback functions.

What about getting the *initial state* of some data ?

Imagine the following case : 

Module A controls data X
Module B would like to be notified of changes of X

Module A: 
1) init X (set it to some initial state - meaningful or default)
2) send 'X_changed'
n) change X
n+1) send 'X_changed'

Module B:
1) connect(callback, 'X_changed')       

B's callback : get copy of X

Everything runs fine as long B's callbacks are initialized before X
contains meaningful data. But if B registers the callbacks after X
changes, B has no possibility to get the new state of X until it changes

There are several possible solutions (re-sending messages to newly
registered callbacks by the dispatcher for some time, register a mandatory
callback on the senders side to request data, notification of the
sender of newly arrived receivers, others ?)

Any suggestions which way to go?


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