Here’s some trivial note on using GObject library.
1. Private members
Recall our definition of Base type:
NOTE: PLEASE READ ALL COMMENT CAREFULLY.
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/* Base object struct */ typedef struct _Base { GTypeInstance parent; /* instance variable, should be hidden */ gint base_instance_i; } Base; /* Base class struct */ typedef struct _BaseClass { GTypeClass parent; /* instance method, used as a virtual method */ void (*base_instance_dump)(struct _Base *instance); } BaseClass; |
It expose the visibility of base_instance_i field. We should keep encapsulation in OOP. GObject library has support for this. We can define the class as:
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/* private data of Base object */ typedef struct _FakeBasePrivate FakeBasePrivate; /* Base object struct */ typedef struct _FakeBase { /* GObject as the first field */ GObject parent; /* private data */ FakeBasePrivate *priv; } FakeBase; /* Base class struct */ typedef struct _FakeBaseClass { /* * The type GObject is supposed to be the base class of other user-defined classes. * - Reference count support. * - Support adding properties to GObject subclasses. * - Support signals for asynchronized event handling like "event" in C#. */ /* GObjectClass as the first field */ GObjectClass parent; /* * Since glib 2.24, there're new functions to keep privacy: * - g_type_add_class_private() * - g_type_class_get_private() */ /* private static field */ gint version; /* private dynamic field */ gchar *author; /* instance method, used as a virtual method */ void (*virtual_dump)(struct _FakeBase *instance); } FakeBaseClass; |
We declare a new FakeBasePrivate struct to contain all private field used in FakeBase type. And the private struct is defined in *.c file, so its internal representation remains invisible. Then in *.c file, we got:
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struct _FakeBasePrivate { gint id; gchar *name; }; static void fake_base_class_init(FakeBaseClass *klass, gpointer data) { // ... /* Registers a private structure for an instantiable type. */ g_type_class_add_private(klass, sizeof(FakeBasePrivate)); // ... } static void fake_base_instance_init(FakeBase *instance, gpointer data) { // ... instance->priv = G_TYPE_INSTANCE_GET_PRIVATE(instance, FAKE_TYPE_BASE, FakeBasePrivate); // ... } |
The private member is malloc in class_init() callback, and is ready to use after invoking instance_init(). When we will use property mechanism to get/set these private field later.
2. Naming convention
Official document: http://library.gnome.org/devel/gobject/stable/gtype-conventions.html. Just follow it to make your code more readable.
All source code is available in my skydrive: http://cid-481cbe104492a3af.office.live.com/browse.aspx/share/dev/TestOO. In the TestGObject-{date}.zip/TestGObject5 folder.