This value is taken from the active row and the column specified
by the [property@Gtk.ComboBox:id-column] property of @combo_box
(see [method@Gtk.ComboBox.set_id_column]).
The returned value is an interned string which means that you can
compare the pointer by value to other interned strings and that you
must not free it.
If the [property@Gtk.ComboBox:id-column] property of @combo_box is
not set, or if no row is active, or if the active row has a %NULL
ID value, then %NULL is returned.
Returns the ID of the active row of @combo_box.
This value is taken from the active row and the column specified by the [property@Gtk.ComboBox:id-column] property of @combo_box (see [method@Gtk.ComboBox.set_id_column]).
The returned value is an interned string which means that you can compare the pointer by value to other interned strings and that you must not free it.
If the [property@Gtk.ComboBox:id-column] property of @combo_box is not set, or if no row is active, or if the active row has a %NULL ID value, then %NULL is returned.