OOP Using GObject (6) – Properties

Properties are supported by the GObject library. To use it, you should override the set_property() and get_property() function in GObjectClass:

NOTE: PLEASE READ ALL COMMENT CAREFULLY.

enum {
    PROP_0,
    PROP_BASE_ID,
    PROP_BASE_NAME
};

static void fake_base_set_property(GObject *object,
    guint property_id, const GValue *value, GParamSpec *pspec) {
    FakeBase *self = FAKE_BASE(object);
    switch (property_id) {
        case PROP_BASE_ID:
            self->priv->id = g_value_get_int(value);
            break;
        case PROP_BASE_NAME:
            g_free(self->priv->name);
            self->priv->name = g_value_dup_string(value);
            break;
        default:
            /* We don't have any other property... */
            G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, pspec);
            break;
    }
}

static void fake_base_get_property(GObject *object,
    guint property_id, GValue *value, GParamSpec *pspec) {
    FakeBase *self = FAKE_BASE(object);
    switch (property_id) {
        case PROP_BASE_ID:
            g_value_set_int(value, self->priv->id);
            break;
        case PROP_BASE_NAME:
            g_value_set_string(value, self->priv->name);
            break;
        default:
            /* We don't have any other property... */
            G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, pspec);
            break;
    }
}

static void fake_base_class_init(FakeBaseClass *klass, gpointer data) {
    // ...
    /* properties */
    GObjectClass *gobject_klass = G_OBJECT_CLASS(klass);
    gobject_klass->set_property = fake_base_set_property;
    gobject_klass->get_property = fake_base_get_property;
    GParamSpec *pspec;
    pspec = g_param_spec_int("base-id", "Base ID", 
        "Set/Get Base ID", -1000, 1000, 0, G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE);
    g_object_class_install_property(gobject_klass, PROP_BASE_ID, pspec);
    pspec = g_param_spec_string("base-name",
        "Base Name", "Set/Get Base Name ", NULL, G_PARAM_READWRITE);
    g_object_class_install_property(gobject_klass, PROP_BASE_NAME, pspec);
    // ...
}

enum {

PROP_0,

PROP_BASE_ID,

PROP_BASE_NAME

};

static void fake_base_set_property(GObject *object,

guint property_id, const GValue *value, GParamSpec *pspec) {

FakeBase *self = FAKE_BASE(object);

switch (property_id) {

case PROP_BASE_ID:

self->priv->id = g_value_get_int(value);

break;

case PROP_BASE_NAME:

g_free(self->priv->name);

self->priv->name = g_value_dup_string(value);

break;

default:

/* We don't have any other property... */

G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, pspec);

break;

}

static void fake_base_get_property(GObject *object,

guint property_id, GValue *value, GParamSpec *pspec) {

FakeBase *self = FAKE_BASE(object);

switch (property_id) {

case PROP_BASE_ID:

g_value_set_int(value, self->priv->id);

break;

case PROP_BASE_NAME:

g_value_set_string(value, self->priv->name);

break;

default:

/* We don't have any other property... */

G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, pspec);

break;

}

static void fake_base_class_init(FakeBaseClass *klass, gpointer data) {

// ...

/* properties */

GObjectClass *gobject_klass = G_OBJECT_CLASS(klass);

gobject_klass->set_property = fake_base_set_property;

gobject_klass->get_property = fake_base_get_property;

GParamSpec *pspec;

pspec = g_param_spec_int("base-id", "Base ID",

"Set/Get Base ID", -1000, 1000, 0, G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE);

g_object_class_install_property(gobject_klass, PROP_BASE_ID, pspec);

pspec = g_param_spec_string("base-name",

"Base Name", "Set/Get Base Name ", NULL, G_PARAM_READWRITE);

g_object_class_install_property(gobject_klass, PROP_BASE_NAME, pspec);

// ...

}

All APIs are clear and easy to use, please refer to the official document. Last but not least, properties can be inherited by derived classes. Here’s my test code:

int main() {
    // ...
    /* Base object */
    FakeBase *base = (FakeBase *)g_object_new(FAKE_TYPE_BASE, "base-id", 111, NULL);
    GValue base_name = { 0 };
    g_value_init(&base_name, G_TYPE_STRING);
    g_value_set_static_string(&base_name, "aaa");
    g_object_set_property(G_OBJECT(base), "base-name", &base_name);
    g_value_unset(&base_name);
    /* Derived object */
    FakeDerived *derived = (FakeDerived *)g_object_new(
        FAKE_TYPE_DERIVED, "base-id", 222, "derived-age", 333, NULL);
    g_object_set(derived, "base-name", "bbb", "derived-hash", "ccc", NULL);
    // ...
}

int main() {

// ...

/* Base object */

FakeBase *base = (FakeBase *)g_object_new(FAKE_TYPE_BASE, "base-id", 111, NULL);

GValue base_name = { 0 };

g_value_init(&base_name, G_TYPE_STRING);

g_value_set_static_string(&base_name, "aaa");

g_object_set_property(G_OBJECT(base), "base-name", &base_name);

g_value_unset(&base_name);

/* Derived object */

FakeDerived *derived = (FakeDerived *)g_object_new(

FAKE_TYPE_DERIVED, "base-id", 222, "derived-age", 333, NULL);

g_object_set(derived, "base-name", "bbb", "derived-hash", "ccc", NULL);

// ...

}

As you see, we can get/set properties one by one or using a parameter list.

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.

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