[gnomemm] error when inheritent from CanvasItem and CanvasEllipse.

["gao chaowei" <chaoweigao hotmail com>]

************file "treeitem.h" ************
#include <gnome--.h>

using namespace Gnome;
class Tree;

#ifndef __TREEITEM_H
#define __TREEITEM_H
class TreeItem : public CanvasItem{
 public:
  Tree * TNode;
  virtual Tree * get_tree() = 0;
};
#endif

#ifndef __TREEELLIPSE_H
#define __TREEELLIPSE_H
class TreeEllipse : public CanvasEllipse, public TreeItem{
 public:
    TreeEllipse(Tree * t=0, const CanvasGroup& parent, double x1, double 
y1, double x2,double y2,const Gtk::string&);
};
#endif

****************file "treeitem.cpp"*****************
#include "treeitem.h"
#include "Tree.h"

//TreeItem=======================================================================


TreeItem TreeItem::TreeItem(Tree * t){
  TNode = t;
}

Tree * get_tree(){
  return TNode;
}



//TreeEllipse====================================================================


TreeEllipse TreeEllipse::TreeEllipse(Tree * t,
       const CanvasGroup& parent, double x1, double y1, double x2,double 
y2,const Gtk::string& color)
       :TreeItem(t), CanvasEllipse(parent,x1,y1,x2,y2){
       set_fill_color(color);
}


****************compilation error**************
In file included from treeitem.cpp:1:
../include/treeitem.h:12: base `Gnome::CanvasItem' with only
non-default constructor in class without a constructor
../include/treeitem.h:20: no unique final overrider for
`SigC::ObjectReferenced::set_dynamic ()' since there two instances of
`Gtk::Object' in `TreeEllipse'
../include/treeitem.h:20: no unique final overrider for
`SigC::ObjectReferenced::reference ()' since there two instances of
`Gtk::Object' in `TreeEllipse'
../include/treeitem.h:20: no unique final overrider for
`SigC::ObjectReferenced::unreference ()' since there two instances of
`Gtk::Object' in `TreeEllipse'


I do not understand the meaning of the error. Anybody can explain and how 
to fix it?


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