gEDA-dev: Hooking into selection changes

[Peter TB Brett]

Hi folks,

I'm busy writing a widget for gschem that needs to update whenever the 
selection changes.

At the moment, there's quite a lot of gschem code that uses the functions from 
libgeda's o_select.c to manipulate the selection directly.

In addition, some libgeda functions manipulate the selection within libgeda.

This causes problems:

 - It's impossible to make my widget work properly, because I can't get any
   sort of guarantee that the necessary callback function will be run when it
   needs to be.
 - The Scheme callback function o_select_run_hooks() suffers from the same
   issue.

In fact, this causes problems for _any_ code that needs to monitor the current 
user selection.

A fairly obvious solution would be to make SELECTION subclass GObject, and 
then to make any function that modifies a selection list emit 
a "selection-changed" signal on it.  Any callback functions could then be 
registered using g_signal_connect() as appropriate.

Anyway, since this would require *extensive* changes to libgeda and gschem, I 
would of course like some indication that it's okay to go ahead with it 
before ploughing in. :)

And any simpler solution would be nice, if such a thing exists!

Peter

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