# File gtk/sample/gtk-demo/list_store.rb, line 83
    def add_columns(treeview)
      # column for fixed toggles
      renderer = Gtk::CellRendererToggle.new
      renderer.signal_connect('toggled') do |cell, path|
        fixed_toggled(treeview.model, path)
      end

      column = Gtk::TreeViewColumn.new('Fixed?',
                                       renderer,
                                       'active' => COLUMN_FIXED)

      # set this column to a fixed sizing (of 50 pixels)
      column.sizing = Gtk::TreeViewColumn::FIXED
      column.fixed_width = 50
      treeview.append_column(column)

      # column for bug numbers
      renderer = Gtk::CellRendererText.new
      column = Gtk::TreeViewColumn.new('Bug number',
                                       renderer,
                                       'text' => COLUMN_NUMBER)
      column.set_sort_column_id(COLUMN_NUMBER)
      treeview.append_column(column)

      # column for severities
      renderer = Gtk::CellRendererText.new
      column = Gtk::TreeViewColumn.new('Severity',
                                       renderer,
                                       'text' => COLUMN_SEVERITY)
      column.set_sort_column_id(COLUMN_SEVERITY)
      treeview.append_column(column)

      # column for description
      renderer = Gtk::CellRendererText.new
      column = Gtk::TreeViewColumn.new('Description',
                                       renderer,
                                       'text' => COLUMN_DESCRIPTION)
      column.set_sort_column_id(COLUMN_DESCRIPTION)
      treeview.append_column(column)
    end