g_object_set_data

["Blowfish" <blow_fish telkom net>]

void
on_button1_clicked (GtkButton       *button,
                 gpointer         user_data)
{
	GtkWidget *tmp;
  GtkWidget *colorselectiondialog1;
	tmp = lookup_widget ((GtkWidget *)button, "window1");
  colorselectiondialog1 = create_colorselectiondialog1 
();
	g_object_set_data ((GObject *)colorselectiondialog1, 
"main_window", tmp);
  gtk_widget_show (colorselectiondialog1);
}

void
on_colorselectiondialog_ok_button1_clicked (GtkButton 
*button, gpointer user_data)
{
	GtkWidget *window;
  window = (GtkWidget *) g_object_get_data ((GObject *) 
button, "main_window");
	gtk_window_set_title ((GtkWindow *)window, "my title");
}

** Gtk-CRITICAL **: file gtkwindow.c: line 822 
(gtk_window_set_title): assertion 
`GTK_IS_WINDOW (window)' failed

how do i fix my code above ? so i can change main_window 
title from colorselection dialog ?
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