Re: PB : Catching delete & cut events / Returning nothing in some functions

[Lars Clausen <lars raeder dk>]

On Fri, 2006-06-02 at 16:22 +0200, SaTuRn 1 wrote:
> Hello, 
>
> I'm currently designing objects for Dia, that can be linked and I'm
> wondering if its possible to catch events (like cut or delete) to
> avoid technical problems ? 
>
> I explain myself. I have a Box (first object) on which I can add
> Connector (second object). This second object should not exist whitout
> being on a Box. But when the user supress a Box its Conectors still
> exist. 
>
> I've seen in the sources that DiaObjects have parent/childrens
> attributes. Will it solve the problem if I used these instead of my
> own current lists ? 
>
> Another related problem, that I have, is I can't forbid the user to
> copy or cut the connector and paste it anywhere on the diagram (major
> problem for me if he does not paste it on a Box...). The "copy"
> problem : if I return NULL in the copy function of the Connector Dia
> crashes. The "cut event" one : I haven't find how to catch the event
> yet. 

You probably want to use the parent/child system.  But it won't prevent
the user from unparenting (can't catch that) and cutting/copying it.
You definitely shouldn't make copy return null, it's used in loading
and/or creating new objects.

Why shouldn't the connectors exist without a box?  Do they use anything
from the box?  In general, Dia doesn't limit the placements of things
much.

-Lars