Re: Subclasses

Ephrem Boudonnet <[email protected]> writes:

> Thanx again for your time. The last CVS version, at the moment,
> doesn't seem to work on my computer, so I'm trying the composition, as
> you've told me to do.

Yesterday I was making some modifications deep inside the proxy library
to get drag and drop working, and I know that at some point the code in
CVS was not working. But I think I've fixed that, so could you check out
the code and try it once more? And if it is still not working post the
error message to the list.

And then about subclassing... With the code in CVS it is now possible to
do subclassing without explicit registering the type with the gobject
system first. Adding slots with instance allocation should work as
expected (but gtk 2.8 is recommended when doing this). It is still not
possible to specialize on gtk "methods" but many methods where this
would be useful, just emit a signal. So by overriding default class
signal handlers, it should be possible to customize the behavior of
subclasses. I've added a macro to do this, with the following syntax:

(define-signal-handler signal-name ((object class) &rest args)
  (do-something)
  (call-next-handler)
  (do-more))

Call-next-handler is more or less equivalent to call-next-method in
standard methods.

So I guess my advise to use composition instead of subclassing isn't
valid any more.

> But I'm trying now to add a slot in a gtk::window.
> Can I do that in the file gtktypes.lisp, in the function
> define-types-by-introspection?
> 
> Something like:
> 
> ...
> 
> ("GtkWindow"
>   :slots
>   ((focus-widget
>     :allocation :virtual
>     :getter "gtk_window_get_focus"
>     :setter "gtk_window_set_focus"
>     :accessor window-focus-widget
>     :initarg :focus-widget
>     :type widget)
> (myslot
>     :allocation :virtual
>     :getter "my_slot_getter"
>     :setter "my_slot_setter"
>     :accessor myslot
>     :initarg 1
>     :type integer)

This is possible, but I wouldn't recommend modifying existing class
definitions as it may become hard to maintain your code. If you don't
want to do subclassing to add new slots, you could use the user data
mechanism to hang arbitrary data on any gobject.

-- 
Espen


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