maemo.org - Talk - HILDON_WINDOW ( ... ) a cast function?

Is there a difference between

HildonWindow *window;
window = HILDON_WINDOW (hildon_window_new());

and

GtkWidget *window;
window = (hildon_window_new());

Essentially.. I'm trying to figure out why there's a need to do the whole HILDON_WINDOW(...) or GTK_CONTAINER(...)?

What's the real purpose of these functions? HILDON_WINDOW or GTK_CONTAINER?

Consider:

Code:

GtkWidget *window;

GtkWidget *button;



window = hildon_window_new ();

button = hildon_button_new_with_text (...);



gtk_container_add (GTK_CONTAINER (window),button);

The signature is:

Quote:

void gtk_container_add (GtkContainer *container,GtkWidget *widget);

In this case, "window" is a pointer to type GtkWidget... so I'm guessing the GTK_CONTAINER serves as some kind of cast (Java background.. forgive me) to convert the GtkWidget to a GtkContainer? My reasoning is since... GtkContainer is a GtkWidget, you need more specificity since the function wants a container, not just any old widget. Is this correct?

Another example I don't quite get is this one...

Quote:

g_signal_connect (G_OBJECT (window), "delete_event",
G_CALLBACK (gtk_main_quit), NULL);

The first parameter is supposed to be a pointer to type GObject... what role does G_OBJECT play here? If this is a cast operation... I'm not used to seeing casts goes this direction. Since GObject is the ultimate superclass.. why would you cast any subclass of GOBject back to GObject?