[Newbie] finalize/dispose and get/set_property

[Laurent JALLET <jallet irit fr>]

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);
 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 ?
//
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 ));
//

 // 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 ***



2.
I've got another question concerning get/set_property() :


I've got a public function to acces mPosition
what should it be ?

Vector3 * camera_getPosition(Camera *a)
{
 return a->priv->mPosition;                           
}

or

Vector3 * camera_getPosition(Camera *a)
{
 Vector3* pos;
 g_object_get (G_OBJECT (a), "position",  &pos, NULL);
 return pos;         
}

or none of these ?
just :
 g_object_get (G_OBJECT (a), "position",  &pos, NULL);
but in this case
should I do  :
{
Vector3 * pos;
g_object_ref(pos);
g_object_get (G_OBJECT (a), "position",  &pos, NULL);
// do things
g_object_unref(pos);
}
?


with

// is it correct ?
static void
camera_get_property (GObject      *object,
                       guint         property_id,
                       GValue       *value,
                       GParamSpec   *pspec)
{

[...]
 case CAMERA_POSITION: {       
   g_value_set_object (value, self->priv->mPosition);  
   break;
[...]    
   
}

// is it correct ?
static void
camera_set_property (GObject      *object,
                       guint         property_id,
                       const GValue *value,
                       GParamSpec   *pspec)
{
 Camera *self = (Camera *) object;
 Vector3 *vtmp;

 switch (property_id) {

   case CAMERA_POSITION: {     
     vtmp = (Vector3 *) g_value_get_object (value);
     camera_setPosition(self, vtmp);
     }
     break;
     
   [...]  
  }   
}   


3.
and what should I do when I'd like to translate the camera ? =>
void camera_localTranslate(Camera *a, Vector3 * t)
// I've writen that using a->priv->mPosition directly (and other members..)

Is it correct to change directly mPosition without using 
set/get_property or  camera_getPosition() / camera_setPosition() ?



I know this questions must look stupid, and there's too much code, but 
I'm quite lost using GObject (and in fact, C programing...).

Thank you by advance

L.J.