RE: Destroying widgets properly

[Murray Cumming Comneon com]

Because you mentioned C++, I should mention that memory mangement is IMHO
easier and more C++-like with gtkmm.

Murray Cumming
www.murrayc.com
murrayc usa net

> -----Original Message-----
> From: gtk-list-admin gnome org 
> [mailto:gtk-list-admin gnome org] On Behalf Of The Surprises
> Sent: Montag, 19. Januar 2004 01:22
> To: Graham Swallow
> Cc: gtk-list gnome org
> Subject: Re: Destroying widgets properly
> 
> 
> Thanks for the feedback.  I still can't get it to work.  I've 
> tried numerous combinations of actions with same results.  
> I've read that you might have to hide() the widget before 
> destroying it to to turn off all events.  Tried it.  Doesn't 
> work.  This is frustrating!
> 
> On Sun, Jan 18, 2004 at 07:54:47PM +0000, Graham Swallow wrote:
> > Me too.
> > 
> > 	My framework is libs_apps_YEAR-MM_DD.tgz at
> > 	http://homepage.ntlworld.com/information-cascade/baks/
> > 	The gtk code is in src/lib_base2/gtk_1/
> > 
> > 	I think I fixed my problem by realising that GTK destroys its
> > 	own widget, THEN tells with the "destroy" callback, so that
> > 	C++ can release its storage WITHOUT REFERRING TO GTK
> > 
> > 	The GTK widget object's memory has been free()d, but you are
> > 	still using it, which either reports "not a valid object",
> > 	or corrupts indirect memory, and the program trips up LATER.
> > 
> > 	When an upper container is deleted, its children get 
> AUTO deleted,
> > 	so you must avoid deleting them, but delete the C++ objects.
> > 
> > 	I also had an issue with signal_disconnect_by_data().
> > 	I'd claim it still happens, but have stopped calling it (leak).
> > 
> > -OR-
> > 
> > 	An alternative phase I went through, was when C++ deleted its
> > 	object, when the GTK object is fully alive.
> > 
> > 	Then GTK calls back, with the deleted objects pointer
> > 	... chaos ...
> > 
> > -Different ways-
> > 
> > 	Different designs require opposite senses. Should your code
> > 	delete the widget before or after GTK? Do you tell it, or
> > 	does it tell you?
> > 
> > 	Reference counts can split widget deconstruction into
> > 	two halves. The DISPLAYED widgets reduction to a skeleton,
> > 	and later free(widget), with the C++ objects delete somewhere.
> > 
> > 	I do tend to NOT do a refcount on GTK objects, even 
> though I keep
> > 	a pointer to them. My excuse is that I should not have received
> > 	a "1" count in the first place, which gets absorbed by the PACK
> > 	action (ASIDE check how TCL does this - it's magically sensible,
> > 	and NOT how Python does it). So I do nothing (and it now works).
> > 
> > 
> >    Graham
> >    Information-Cascade (at) ntlworld.com
> > 
> > 
> > > Message: 1
> > > Date: Sun, 18 Jan 2004 00:42:46 -0800
> > > From: The Surprises <thesurprises1 comcast net>
> > > To: gtk-list gnome org
> > > Subject: Destroying widgets properly
> > > 
> > > Hello,
> > > I am getting mysterious and inconsistent crashes in my 
> gtk program 
> > > (ie it isn't crashing in the same spot every time), and I 
> believe it 
> > > has something to do with how I am destroying a set of widgets.  I 
> > > have an hbox (HB) packed into a vbox (VB).  HB has many widgets 
> > > packed inside of it, most of which are also created/maintained in 
> > > their own C++ classes.  One of the widgets is a 
> GnomeCanvas, and it 
> > > itself has many GnomeCanvasItem children, nearly each 
> maintained in 
> > > seperate C++ classes as well.  At times, I need to 
> entirely remove 
> > > HB and all of it's children including the canvas and all of it's 
> > > children. I then recreate everything from scratch and 
> pack into VB.  
> > > Actually the destroy seems to work OK.  It is when I try 
> to recreate 
> > > all the widgets that I get the core dump.
> > > 
> > > I tried having each class destructor first delete it's children 
> > > (with a 'delete'), then destroy it's own widget (in the 
> case of the 
> > > GnomeCanvasItems, using GTK_OBJECT_DESTROY and casting the 
> > > CanvasItem). I thought this made the most sense since you want to 
> > > delete the children first before you delete the parent or you'll 
> > > have children pointing to parents that no longer exist.  I also 
> > > tried reversing the order as well but get the same result.  I get 
> > > error messages like this:
> > > 
> > > GLib-GObject-WARNING **: invalid uninstantiatable type 
> `gint64' in 
> > > cast to `GtkObject'
> > > 
> > > Gtk-CRITICAL **: file gtkobject.c: line 358
> > > (gtk_object_destroy): assertion `GTK_IS_OBJECT (object)' failed
> > > 
> > > GLib-GObject-WARNING **: invalid cast from `(null)' to `GtkObject'
> > > 
> > > Gtk-CRITICAL **: file gtkobject.c: line 358
> > > (gtk_object_destroy): assertion `GTK_IS_OBJECT (object)' failed
> > > 
> > > 
> > > I tried just doing a destroy on HB but get the same results.  It 
> > > seems like I'm leaving something behind.  It works a few 
> times, then 
> > > crashes. Or it crashes on the first try.
> > > 
> > > Thanks for any help
> > > Jason
> > > 
> > > 
> > > --__--__--
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