rem: if (preference_selected != -1)
add: if ( preference_selected != NOT_A_PAGE )
context: gboolean selectionne_liste_preference ( GtkTreeSelection *selection,					GtkTreeModel *model ){  GtkTreeIter iter;  GValue value = {0, };  GtkWidget widget;  if (! gtk_tree_selection_get_selected (selection, NULL, &iter))    return;  gtk_tree_model_get_value (model, &iter, 1, &value);  /*   if (preference_selected) */  /*     { */  /*       gtk_widget_hide_all(preference_selected); */  /*       g_object_ref(preference_selected); /\* GRUIK *\/ */  /*       gtk_container_remove (GTK_CONTAINER (preference_frame), preference_selected); */  /*     } */  preference_selected = g_value_get_int(&value);  if (preference_selected != -1)    {      gtk_notebook_set_page (preference_frame, preference_selected);    }  g_value_unset (&value);  return FALSE;}