Re: Gtk::Widget as virtual base

[Antonio Coralles <noche suapie reflex at>]

jyotirmoy bhattacharya wrote:

> I want to use an abstract class derived from Gtk::Widget and then
> derive different classes which use particular widgets to display
> themselves.
>
> That is, I want to do something like
>
> class vwidget: public virtual Gtk::Widget
> {
>  public:
>   virtual void magic()=0;
> };
>
> class mywidget: public vwidget, public Gtk::HBox
> {
>  public:
>   void magic() {x=1;}
>  private:
>   int x;
> };
>
> mywidget m;
>
> But when I compile this I get the following errors:
> document.h:86: error: no unique final overrider for `virtual void
> Glib::ObjectBase::destroy_notify_()' in `mywidget'
> document.h:86: error: no unique final overrider for `virtual void
> Glib::ObjectBase::set_manage()' in `mywidget'
> document.h:86: error: no unique final overrider for `virtual void
> Glib::ObjectBase::destroy_notify_()' in `mywidget'
> document.h:86: error: no unique final overrider for `virtual void
> Glib::ObjectBase::set_manage()' in `mywidget'
>
The problem is that Gtk::HBox is also an Gtk::Widget and thus for
example Gtk::Hbox has methods like Gtk::Widget like set_manage(),
destroy_notify_(), ... . How can the compiler know if you want to use
Gtk::Widget::set_manage() or Gtk::HBox::set_manage() in your mywidget
class ? If you really want to do this, you have to make that decission
yourself for every method the compiler complains about.

class mywidget: public vwidget, public Gtk::HBox
{
 public:
  void magic() {x=1;}

  // this are unique final overriders
  void destroy_notify() { vwwidget::destroy_notify(); }
  void set_manage() { Gtk::HBox::set_manage(); }
  // ....
 
 private:
  int x;
};

Maybe may also be interested in
http://www.parashift.com/c++-faq-lite/multiple-inheritance.html#faq-25.11.

Hope this helps,
Antonio

> I am using gtkmm 2.4 and g++ 3.4.2
>
> Not making Gtk::Widget virtual in the definition of vwidget leads to
> the same errors and
> I don't think that would solve my problem anyway.
>
> I would be grateful if the subscribers of this list can suggest a way
> out of my problem.
>
> --Jyotirmoy
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