@Override
 protected Widget attachEdgeWidget(Edge edge) {
   Widget widget = WidgetFactory.getDefault().createWidget(this, edge);
   addChild(widget);
   return widget;
 }
 @Override
 protected Widget attachNodeWidget(Vertex node) {
   Widget widget = WidgetFactory.getDefault().createWidget(this, node);
   addChild(widget);
   return widget;
 }