gobject instantiation

MamanBar *bar = g_object_new (MAMAN_TYPE_BAR, NULL);

first instantiation of an object,

        (1) maman_b_class_init is invoked after any mam_b_base_class_init

          --->make sure the class structure of this new object is correctly initialized

-->setup the class' own methods. (e.g. the constructor method is the overridden method,i.e. Set to mam_bar_constructor).

After g_object_new has obtained a reference to an initialized class structure

       (2)invokes its constructor method(maman_bar_constructor) to create an instance of the new object.

       (3)mam_bar_consturctor chains up parent's constructor

       (4)g_object_constructor is invoked :

            a. allocates the object's instance's buffer through g_type_create_instance

                                                                                    ==>where instance_init is invoked

            b.set the construction properties(i.e. The properties given to g_object_new)

1. #define MAMAN_TYPE_BAR                  (maman_bar_get_type ())
2. #define MAMAN_BAR(obj)                  (G_TYPE_CHECK_INSTANCE_CAST ((obj), MAMAN_TYPE_BAR, MamanBar))
3. #define MAMAN_BAR_CLASS(klass)          (G_TYPE_CHECK_CLASS_CAST ((klass), MAMAN_TYPE_BAR, MamanBarClass))
4. #define MAMAN_IS_BAR(obj)          (G_TYPE_CHECK_INSTANCE_TYPE ((obj), MAMAN_TYPE_BAR))
5. #define MAMAN_IS_BAR_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), MAMAN_TYPE_BAR))
6. #define MAMAN_BAR_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), MAMAN_TYPE_BAR, MamanBarClass))
8. typedef struct _MamanBar MamanBar;
9. typedef struct _MamanBarClass MamanBarClass;
11. struct _MamanBar {
12.   GObject parent;
13.   /* instance members */
14. };
16. struct _MamanBarClass {
17.   GObjectClass parent;
19.   /* class members */
20. };
22. /* used by MAMAN_TYPE_BAR */
23. GType maman_bar_get_type (void);
25. static GObject *
26. maman_bar_constructor (GType                  type,
27.                        guint                  n_construct_properties,
28.                        GObjectConstructParam *construct_properties)
29. {
30.   GObject *obj;
32.   {
33.     /* Invoke parent constructor. */
34.     MamanBarClass *klass;
35.     GObjectClass *parent_class;  
36.     klass = MAMAN_BAR_CLASS (g_type_class_peek (MAMAN_TYPE_BAR));
37.     parent_class = G_OBJECT_CLASS (g_type_class_peek_parent (klass));
38.     obj = parent_class->constructor (type,
39.                                      n_construct_properties,
40.                                      construct_properties);
41.   }
42.   
43.   /* do stuff. */
45.   return obj;
46. }
48. static void
49. maman_bar_instance_init (GTypeInstance   *instance,
50.                          gpointer         g_class)
51. {
52.   MamanBar *self = (MamanBar *)instance;
53.   /* do stuff */
54. }
56. static void
57. maman_bar_class_init (gpointer g_class,
58.                       gpointer g_class_data)
59. {
60.   GObjectClass *gobject_class = G_OBJECT_CLASS (g_class);
61.   MamanBarClass *klass = MAMAN_BAR_CLASS (g_class);
63.   gobject_class->constructor = maman_bar_constructor;
64. }
66. GType maman_bar_get_type (void)
67. {
68.   static GType type = 0;
69.   if (type == 0) {
70.     static const GTypeInfo info = {
71.       sizeof (MamanBarClass),
72.       NULL,   /* base_init */
73.       NULL,   /* base_finalize */
74.       maman_bar_class_init,   /* class_init */
75.       NULL,   /* class_finalize */
76.       NULL,   /* class_data */
77.       sizeof (MamanBar),
78.       0,      /* n_preallocs */
79.       maman_bar_instance_init    /* instance_init */
80.     };
81.     type = g_type_register_static (G_TYPE_OBJECT,
82.                                    "MamanBarType",
83.                                    &info, 0);
84.   }
85.   return type;
86. }