# File gtk/sample/gtk-demo/editable_cells.rb, line 102
    def add_columns(treeview)
      model = treeview.model

      # number column
      renderer = Gtk::CellRendererText.new
      renderer.signal_connect('edited') do |*args|
        cell_edited(*args.push(model))
      end
      treeview.insert_column(-1, 'Number', renderer,
                             {
                               :text => COLUMN_NUMBER,
                               :editable => COLUMN_EDITABLE,
                             })
      def renderer.column
        COLUMN_NUMBER
      end

      # product column
      renderer = Gtk::CellRendererText.new
      renderer.signal_connect('edited') do |*args|
        cell_edited(*args.push(model))
      end
      def renderer.column
        COLUMN_PRODUCT
      end
      treeview.insert_column(-1, 'Product', renderer,
                             {
                               :text => COLUMN_PRODUCT,
                               :editable => COLUMN_EDITABLE,
                             })
    end