Re: Question on emission hooks

["Nickolay V. Shmyrev" <nshmyrev yandex ru>]

Hello.

Sorry for style of my first answer, it seems that you have quite old
glib, because now (in 2.4.0 )it is impossible to g_signal_lookup on
G_TYPE_OBJECT, since it is not G_TYPE_IS_INSTANTIABLE, that's why I
thought that you are trying to to add emission hook to "notify" signale
of your type GWP_TYPE_SHIP, not G_TYPE_OBJECT. 

Even if you can get signal_id, it is not clear, that you can add
emission hook to that signal, because signal can have flag
G_SIGNAL_NO_HOOKS. The "notify" signal of g_object is exactly such
signal, that is why you get warning message. 



Look at glib sources:



  gobject_signals[NOTIFY] =
    g_signal_new ("notify",
                  G_TYPE_FROM_CLASS (class),
                  G_SIGNAL_RUN_FIRST | G_SIGNAL_NO_RECURSE |
G_SIGNAL_DETAILED | G_STRUCT_OFFSET (GObjectClass, notify),
                  NULL, NULL,
                  g_cclosure_marshal_VOID__PARAM,
                  G_TYPE_NONE,
                  1, G_TYPE_PARAM);




g_signal_add_emission_hook (guint               signal_id,
                            GQuark              detail,
                            GSignalEmissionHook hook_func,
                            gpointer            hook_data,
                            GDestroyNotify      data_destroy)
{
  static gulong seq_hook_id = 1;
  SignalNode *node;
  GHook *hook;
  SignalHook *signal_hook;
                                                                                
  g_return_val_if_fail (signal_id > 0, 0);
  g_return_val_if_fail (hook_func != NULL, 0);
                                                                                
  SIGNAL_LOCK ();
  node = LOOKUP_SIGNAL_NODE (signal_id);
  if (!node || node->destroyed || (node->flags & G_SIGNAL_NO_HOOKS))
    {
      g_warning ("%s: invalid signal id `%u'", G_STRLOC, signal_id);
      SIGNAL_UNLOCK ();
      return 0;
    }

Otherwise, all goes fine:

#include <gtk/gtk.h>

static gboolean
clicked_emission_hook (GSignalInvocationHint *ihint,
      guint                  n_param_values,
      const GValue          *param_values,
      gpointer               data)
{
  g_message ("HOOK!!!");
  return TRUE;
}

static gboolean
on_clicked (GObject *button,   gpointer data)
{
  g_message ("ACTIVATE!!!");
  return TRUE;
}


int main (int argc, char *argv[]) {
  
  GtkWidget *window;
  GtkWidget *button;
  
  gtk_init (&argc, &argv);

  
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  button = gtk_button_new_with_label ("Push me");
  gtk_container_add (GTK_CONTAINER(window), button);
  gtk_widget_show_all (window);    

  g_signal_add_emission_hook (g_signal_lookup("clicked",
GTK_TYPE_BUTTON),
  0,  clicked_emission_hook, NULL, NULL);
  
  g_signal_connect (G_OBJECT(button), "clicked", G_CALLBACK(on_clicked),
NULL);
  
  gtk_main ();
  
  return 0;
}