Re: custom treemodel?

["Andrew E. Makeev" <andrew solvo ru>]

Jonathon Jongsma wrote:

> > > In fact i have a skeleton like this implemented to play around with,
> > > but I can't get it to instantiate.  When I call the
> > > MyListModel::create() function, I keep getting errors like this:
> > >
> > > glibmm-CRITICAL **: Glib::Interface::Interface(const
> > > Glib::Interface_Class&): assertion `gobject_ != 0' failed
> >
> > Maybe you need to call the Glib::Object (or maybe ObjectBase, I forget)
> > constructor differently, if the example does that. Remember our 
> > discussion
> > about virtual inheritance.
>
>
> Well, I call it exactly the same way as the example does it.  The main
> difference is of course that I'm not actually instantiating that
> class, but one derived from it.
>
> > Glib interfaces are implemented by GObjects. That's just how the GObject
> > type system works. So we need a GObject type, and each of our class
> > instances will need an instance of that GObject type.
>
>
> Right.  Perhaps I just need to bite the bullet and brush up on some
> GObject fundamentals.  gtkmm is very good about hiding most of the
> GObject ugliness, but it seems like this is one instance where I may
> need some additional background.
>
> > > Or should I be doing the GObject type registration in the most derived
> > > class (MyListModel) instead of CustomTreeModel?  Or is my approach
> > > just flawed in some basic way?
> >
> > Yes, I suspect that you might need to call the Object constructor in the
> > most derived class. And that is where you are doing the type 
> > registration,
> > I  think.
>
>
> OK, here are some results of some trial-and-error experimentation.
> See if you can make sense of them :)
>
> No Warnings:
> ===========
> CustomTreeModel : public Gtk::TreeModel
> MyListModel : public CustomTreeModel<>, virtual public Glib::Object
>  - calls Object, ObjectBase constructor
>
> CustomTreeModel : public Gtk::TreeModel, virtual public Glib::Object
>  - calls Object, ObjectBase constructor
> MyListModel : public CustomTreeModel<>, virtual public Glib::Object
>  - calls Object, ObjectBase constructor
>
> CustomTreeModel : public Gtk::TreeModel, virtual public Glib::Object
>  - calls Object, ObjectBase constructor
> MyListModel : public CustomTreeModel<>, virtual public Glib::Object
>
> CustomTreeModel : public Gtk::TreeModel, virtual public Glib::Object
>  - calls Object, ObjectBase constructor
> MyListModel : public CustomTreeModel<>
>
> Gives Warning:
> ============
> CustomTreeModel : public Gtk::TreeModel, public Glib::Object
>  - calls Object, ObjectBase constructor
> MyListModel : public CustomTreeModel<>
>
> CustomTreeModel : public Gtk::TreeModel
> MyListModel : public CustomTreeModel<>, public Glib::Object
>  - calls Object, ObjectBase constructor
>
> Error, crash
> ============
> CustomTreeModel : public Gtk::TreeModel, public Glib::Object
>  - calls Object, ObjectBase constructor
> MyListModel : public CustomTreeModel<>, public Glib::Object
>  - calls Object, ObjectBase constructor
>
>
> So it seems that when I use virtual inheritance, the warnings go away.
> But I can't quite figure out why...  I haven't gotten around to
> implementing enough of the class to see whether the model actually
> works correctly, but the warnings are gone.  Now the question -- which
> of the four non-warning choices is correct, if any?
That is may way of creating custom models:

   class CommonModel // class with common data handling and sorting 
methods for my data-container
   {...}

   class  DataListTreeModel
   : public Glib::Object
   , public Gtk::TreeModel
   , public Gtk::TreeSortable
   , public CommonModel
   {...}

   class BROWSER_DLL_EXP_IMP DataTreeTreeModel
   : public Glib::Object
   , public Gtk::TreeModel
   , public Gtk::TreeSortable
   , public CommonModel
   {...}

   CommonModel::CommonModel( DataSet* ds )
   {...}

   DataListTreeModel::DataListTreeModel( DataSet* ds )
   : Glib::ObjectBase( typeid( DataListTreeModel ) )
   , Glib::Object()
   , CommonModel( ds )
   {...}

   DataTreeTreeModel::DataTreeTreeModel( DataSet* ds )
   : Glib::ObjectBase( typeid( DataTreeTreeModel ) )
   , Glib::Object()
   , CommonModel( ds )
   {...}


there is no warning nor crash.

Regards,
-andrew