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List: gtk-app-devel
Subject: Re: [Newbie] finalize/dispose and get/set_property
From: Stefan Kost <ensonic () hora-obscura ! de>
Date: 2005-04-28 11:21:18
Message-ID: 4270C72E.3050400 () hora-obscura ! de
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Hi Laurent,
please see inline comments.
> hi all,
>
> I'm using GObject to do "Object Programing in C", I'm not using GTK.
> I search in the mailing-list archive and I didn't get what I'd like.
>
> I've got pragmatic questions, quite "simple" (although I don't
> understand), in order to have basics for doing deeper things :
>
> 1.
> I know it's a redundant question but I still don't understand how to use
> finalize() and dispose().
> I understand that dispose() is called when a g_object_unref() is called
> and that finalize() is called when the last g_object_unref() is called.
>
> I've got a GObject Camera, with :
>
> struct _CameraPrivate {
> Vector3 * mPosition;
> // and other members gboolean dispose_has_run;
> };
>
> Vector3 is a GObject, with no private struct (<- no need)
> struct _Vector3 {
> GObject parent;
> gfloat x, y, z;
>
> gboolean dispose_has_run;
> };
>
>
> I don't know what to do when I unref a camera : g_object_unref (G_OBJECT
> (camera));
> I'd like to unref camera->self->mPosition, but when? and How ?
> And when do I free mPosition (g_free (self->priv->mPosition)) ?
> (I don't use signal)
>
> I' tried to unref(mPosition) in the camera_dispose(), but i've got an
> error.
>
>
> Here is my code :
>
>
> static void
> camera_instance_init (GTypeInstance *instance,
> gpointer g_class)
> {
> Camera *self = (Camera *)instance;
> self->priv = g_new (CameraPrivate, 1);
>
> self->priv->mPosition = g_new (Vector3, 1);
if the Vector3 thing is a GObject this should be
self->priv->mPosition = g_object_new(<the Vector3 type>,NULL);
> vector3_set(self->priv->mPosition, -1.15, 32.0, 43.75); // or whatever
>
> self->priv->dispose_has_run = FALSE;
> }
>
> //
> // what should I do ?
> // replace mPosition by v ? ( => unref(mPosition) & ref(v) )
> // or like I do just change the members x, y and z ?
> //
here I recommend to use GObject properties. Reread the gobjet tutorial and watch
out of g_object_class_install_property() and the _set_property(),
_get_property() methods
> void camera_setPosition(Camera *a, Vector3 * v)
> {
> a->priv->mPosition->x = v->x;
> a->priv->mPosition->y = v->y;
> a->priv->mPosition->z = v->z;
> }
>
>
> static void
> camera_dispose (GObject *obj)
> {
> Camera *self = (Camera *)obj;
>
> if (self->priv->dispose_has_run) {
> // If dispose did already run, return.
> return;
> }
> // Make sure dispose does not run twice
> self->priv->dispose_has_run = TRUE;
>
> g_print("|| camera dispose ||\n");
>
> // In dispose, you are supposed to free all types referenced from this
> // object which might themselves hold a reference to self. Generally,
> // the most simple solution is to unref all members on which you own a
> // reference.
>
> //
> // that why I try to unref mPosition
> //
> g_object_unref (G_OBJECT ( self->priv->mPosition ));
> //
if you turn the g_new() in init() into a g_object_new() then this will work.
As a rule of the thumb, release all references in dispose() and release all
memory in finalize().
>
> // Chain up to the parent class
> G_OBJECT_CLASS (parent_class)->dispose (obj);
> }
>
> static void
> camera_finalize (GObject *obj)
> {
> Camera *self = (Camera *)obj;
>
> g_print("*** camera finalize ***\n");
>
> //
> // what sould I do ? g_free or g_object_unref (mPosition) ?
> // g_free (self->priv->mPosition);
> // g_object_unref (G_OBJECT (self->priv->mPosition) );
> //
>
> g_free (self->priv);
>
> /* Chain up to the parent class */
> G_OBJECT_CLASS (parent_class)->finalize (obj);
> }
>
>
>
> result =>
>
> || camera dispose ||
>
> (process:15709): GLib-GObject-WARNING **: invalid unclassed pointer in
> cast to `GObject'
>
> (process:15709): GLib-GObject-CRITICAL **: g_object_unref: assertion
> `G_IS_OBJECT (object)' failed
> *** camera finalize ***
>
Stefan
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