Re: gtk-2 bug, inconsistency or simply misunderstanding on my side ?

[Olexiy Avramchenko <ath beast stu cn ua>]

Olivier Fourdan wrote:

> Hi all,
>
> I've seem some behaviour in gkt that I don't understand well.
>
> The problem shows like this :
>
> create a container (a frame)
> add another container (another frame) inside the first one.
> at last, add a widget to the last container.
>
> It looks like this :
>
> container1
>    +-> container2
>             +->widget
>
> It happens that, when destroying container2 the widget is freed twice
> (even if the widget is *not* destroyed explicitely by the program).
>
> This is because (if I understand well) when destroying the container,
> the widget is removed from the container first, so its reference count
> is decremented and reach zero, so it gets automatically free, and then
> the widget is freed again because its parent is destroyed.
>
> The (easy to tell, hard to find) workarround is to force a
> g_object_ref() on the widget at creation. This way, the
> gtk_container_remove performed automatically doesn't free the widget, so
> it gets freed only once.
>
> Do all this make any sense ? Am I missing something obvious here ?
Hello, Olivier

Looks like you're killing the second container by g_object_unref().
Use gtk_widget_destroy instead(). Look at the little prog I've attached.

Olexiy


#include <stdio.h>
#include <gtk/gtk.h>


static void (*button_class_finalize)(GObject *object);


static void on_destroy(GtkWidget *widget)
{
        printf("%p::destroy\n", widget);
}

static void on_finalize(GObject *object)
{
        printf("%p::finalize\n", object);
        button_class_finalize(object);
}

static void frame_slayer(GtkWidget *button, GtkWidget **frame)
{
        if (*frame) {
                gtk_widget_destroy(*frame);
                *frame = NULL;
        }
        else    printf("what frame ?\n");
}

int main(int argc, char **argv)
{
GtkWidget *window;
GtkWidget *vbox;
GtkWidget *frame1,*frame2;
GtkWidget *button;
    
        gtk_init(&argc, &argv);

        window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
        g_signal_connect(G_OBJECT(window), "destroy", G_CALLBACK(gtk_main_quit), window);
        gtk_container_set_border_width(GTK_CONTAINER(window), 8);

        vbox = gtk_vbox_new(FALSE, 0);
        gtk_container_add(GTK_CONTAINER(window), vbox);

        frame1 = gtk_frame_new(" <frame 1> ");
        gtk_container_add(GTK_CONTAINER(vbox), frame1);
        gtk_container_set_border_width(GTK_CONTAINER(frame1), 8);

        frame2 = gtk_frame_new(" <frame 2> ");
        gtk_container_add(GTK_CONTAINER(frame1), frame2);
        gtk_container_set_border_width(GTK_CONTAINER(frame2), 8);

        button = gtk_button_new_with_label(" test widget ");
        gtk_container_add(GTK_CONTAINER(frame2), button);
        g_signal_connect(G_OBJECT(button), "destroy", G_CALLBACK(on_destroy), NULL);

        /* a little hack used to override the GObject::finalize method
           (creation of the new widget is much more lines of code)
        */
        button_class_finalize = G_OBJECT_CLASS(g_type_class_peek(GTK_TYPE_BUTTON))->finalize;
        G_OBJECT_CLASS(g_type_class_peek(GTK_TYPE_BUTTON))->finalize = on_finalize;

        button = gtk_button_new_with_label("slay the second frame");
        gtk_container_add(GTK_CONTAINER(vbox), button);
        g_signal_connect(G_OBJECT(button), "clicked", G_CALLBACK(frame_slayer), &frame2);

        gtk_widget_show_all(window);
        
        gtk_main();

        return 0;
}