Re: [gtk-list] Gtk+ Signal question

[Tim Janik <timj gtk org>]

On Mon, 20 Jul 1998, Michael Lausch wrote:

> 
> Suppose i have a class which emits two signals. `error' and
> `warning'. I want to have a defautl action for this signals, if the
> user didn't connect any actions to the signal. The default action
> should not be executed, if the user wants to handle the signals. If no 
> actions are connected to the signals, the default action shoudl be
> executed.
> 
> How can this be done?

implement a handler for that warning function:

static void
my_handler (GtkWidget *widget)
{
  printf ("hey, i guess i should warn you!\n");
}

and in class_init you do

  widget_signals[DEBUG_MSG] =
    gtk_signal_new ("warning_msg",
                    GTK_RUN_LAST,
                    object_class->type,
                    GTK_SIGNAL_OFFSET (GtkWidgetClass, warning_msg),
                    gtk_signal_default_marshaller,
                    GTK_TYPE_NONE, 0);
  widget_class->warning_msg = my_handler;

now when you later connect to this signal, your handler needs to stop the
emission, so the classes default handler doesn't get called:

void
user_handler (GtkWidget *widget, gpointer data)
{
  printf ("warning ignored!\n");
  gtk_signal_emit_stop_by_name (GTK_OBJECT (widget), "warning_msg");
}

that would be the usual way to do this. however another approach exists:

class_init:

  widget_signals[DEBUG_MSG] =
    gtk_signal_new ("warning_msg",
                    GTK_RUN_FIRST,
                    object_class->type,
                    GTK_SIGNAL_OFFSET (GtkWidgetClass, warning_msg),
                    gtk_signal_default_marshaller,
                    GTK_TYPE_NONE, 0);
  widget_class->warning_msg = my_handler;

and the default handler:

static void
my_handler (GtkWidget *widget)
{
  /* check for pending handlers on this signal:
  */
  if (!gtk_signal_handler_pending (GTK_OBJECT (widget), widget_signals[DEBUG_MSG], FALSE))
  {
    printf ("hey, i guess i should warn you!\n");
  }
}

note the differences in the signal run type during signal creation. in the
former example we use RUN_LAST so that our handler can be skipped when the
emisison is stopped at the users request. in the latter we use RUN_FIRST and
decide what to do in this function by checking whether there are actually
user handlers pending or not.

> --
> Michael Lausch/g.a.m.s. edv dienstleistungen gmbh
> See my web page <http://www.gams.net/~mla> or query PGP key server for PGP key.
> "Reality is that which, when you stop believing in it, doesn't go away".
>                 -- Philip K. Dick
> 
> -- 
> To unsubscribe: mail -s unsubscribe gtk-list-request@redhat.com < /dev/null
> 
> 

---
ciaoTJ