Re: refptr and this

[Jonathon Jongsma <jonathon quotidian org>]

On Sun, 2008-02-17 at 10:58 +0100, Murray Cumming wrote:
> On Fri, 2008-02-15 at 23:36 -0600, Jonathon Jongsma wrote:
> >  child->set_parent(Glib::RefPtr<Item>(this));
> > Except this seems to cause refcounting problems and the program crashes.
> 
> The RefPtr constructor does not take a reference, so you need to do
> RefPtr<Item>(this, true). I think it's that simple.
> 
> Murray.

Well, the reason I didn't do this is because I don't believe you're
supposed to take a reference when you set the parent.  If you did, I
think you would end up with circular references and the objects would
never get destroyed (e.g. child holds a reference to parent and parent
holds a reference to child).  

For reference, here's the C implementation for set_parent in ItemSimple:

static void
goo_canvas_item_simple_set_parent (GooCanvasItem  *item,
				   GooCanvasItem  *parent)
{
  GooCanvasItemSimple *simple = (GooCanvasItemSimple*) item;
  GooCanvas *canvas;

  simple->parent = parent;
  canvas = parent ? goo_canvas_item_get_canvas (parent) : NULL;
  goo_canvas_item_set_canvas (item, canvas);
  simple->need_update = TRUE;
  simple->need_entire_subtree_update = TRUE;
}

-- 
Jonner