Re: gtkmm-4: Widget wrappers can't be deleted like in gtkmm-3

On Fri, 1 Dec 2017 13:35:01 +0100
Kjell Ahlstedt <kjellahlstedt gmail com> wrote:
Changes in gtk+-4 make it impossible to delete C++ widget wrappers
like it's done in Gtk::Object::~Object() and 
Gtk::Object::_release_c_instance(). See How can we do
it in gtkmm-4? Comments ans suggestions are welcome.
I guess one approach is to retain the Gtk::Widget/Gtk::Window class for
top level widgets, on which gtk_widget_destroy() can be called with the
correct result, and to manage everything else by operating only on the
GObject reference count (as with Glib::RefPtr) and by adding and
removing widgets from their containers.  That is essentially (and
somewhat fortuitously) what a wrapper of my own which I sometimes use
does, and what (as I understand it) C code is supposed to do with GTK+4.

It would however give rise to a fearsome amount of work and a complete
redesign of the interfaces, which I imagine would not be welcome to
gtkmm users.

There may be an easier fix. See Gtk::Object::_release_c_instance(): Don't release if in a container Don't release the C instance, if it's a widget in a container widget. Just steal the GQuark that points from the C instance to the C++ wrapper, and accept that a new wrapper is later created, if necessary. Nowadays it's difficult to know which container the widget has been added to. It's not necessarily the one returned by gtk_widget_get_parent(). Bug 773642 comments 20-22. See also gtk+ bug 786048 comment 5. With this patch all demo programs run without segfault and without messages that relate to destruction of C instances. Kjell

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