about button_press_signal?

["changan" <heface hotmail com>]

/*function first*/
#include <gtk/gtk.h>
#include <stdio.h>
gint response(GtkWidget *widget,GdkEvent* event,gpointer data)
{
        printf("button was pressed\n");
}
int main(int argc,char *argv[])
{
        GtkWidget *window;

        gtk_init(&argc,&argv);
        window=gtk_window_new(GTK_WINDOW_TOPLEVEL);
        gtk_widget_set_usize(window,300,200);

gtk_signal_connect(GTK_OBJECT(window),"delete_event",GTK_SIGNAL_FUNC(gtk_mai
n_quit),NULL);
        gtk_widget_show(window);


gtk_signal_connect_object(GTK_OBJECT(window),"button_press_event",GTK_SIGNAL
_FUNC(response),NULL);

        gtk_main();
        exit(0);
}

/*function second*/
#include <gtk/gtk.h>
#include <stdio.h>
gint response(GtkWidget *widget,GdkEvent* event,gpointer data)
{
        printf("button was pressed\n");
}
int main(int argc,char *argv[])
{
        GtkWidget *window;
        GtkWidget *fixed;

        gtk_init(&argc,&argv);
        window=gtk_window_new(GTK_WINDOW_TOPLEVEL);
        gtk_widget_set_usize(window,300,200);

gtk_signal_connect(GTK_OBJECT(window),"delete_event",GTK_SIGNAL_FUNC(gtk_mai
n_quit),NULL);
        gtk_widget_show(window);

        fixed=gtk_fixed_new();
        gtk_container_add(GTK_CONTAINER(window),fixed);
        gtk_widget_show(fixed);


gtk_signal_connect_object(GTK_OBJECT(window),"button_press_event",GTK_SIGNAL
_FUNC(response),NULL);

        gtk_main();
        exit(0);
}

The second function can receive button_press_event and the first can
not,why?
The widget that inherit GtkWidget could catch button_press_event,didn't so?
In second function I replaced GtkFixed by GtkBox . Then it can't catch
button_press_event.
Who can explain for me ?
Thank you!