Re: Interfaces and properties, signals

[jrb redhat com]

Tim Janik <timj gtk org> writes:

> On Mon, 12 Mar 2001, Bill Haneman wrote:
> 
> > Hi Tim:
> 
> > I've come across a use case with GTypeInterface that I can't seem to
> > find an example of, and wonder if you could answer a couple of
> > questions.
> > 
> > We have two properties ("accessible_text" and "caret") and a signal
> > ("caret_moved") that we'd like to associate with implementors of a
> > particular interface (AtkTextIface).
> > 
> > Two questions come to mind:
> > 
> > 1) Is it possible to register properties and signals on interface
> > classes?
> > 2) Is there a clean way of doing it ;-)
> 
> yes and no ;)
> as owen already outlined, we decided against per-interface properties,
> at least for 2.0, because it isn't at all obvious how to do that.
> for signals, yes, they should run fine on interfaces, you basically
> do the the same way you do them on a normal class (i believe jonathan
> even uses interface signals already in his tree backends).

I do.  One of the peculiarities of interface signals is that there is no
really good place to set the signals up.  I've been using the base_init
slot to do so, which is called multiple times, so I have the following
code:

static void
gtk_tree_model_base_init (gpointer g_class)
{
  static gboolean initialized = FALSE;

  if (! initialized)
    {
      /* set up signals... */
      initialized = TRUE;
    }
}

GtkType
gtk_tree_model_get_type (void)
{
  static GtkType tree_model_type = 0;

  if (! tree_model_type)
    {
      static const GTypeInfo tree_model_info =
      {
        sizeof (GtkTreeModelIface), /* class_size */
	gtk_tree_model_base_init,   /* base_init */
	NULL,		/* base_finalize */
      };

      tree_model_type = g_type_register_static (G_TYPE_INTERFACE, "GtkTreeModel", &tree_model_info, 0);
      g_type_interface_add_prerequisite (tree_model_type, G_TYPE_OBJECT);
    }

  return tree_model_type;
}

Hope this helps,
-Jonathan