content: function init()
      m.category_list = m.top.findNode("category_list")
      m.top.observeField("visible", "on_visible_change")
      m.category_list.setFocus(true)
  end function
  
  sub on_visible_change()
      if m.top.visible then
          m.category_list.setFocus(true)
      end if
  end sub
  
  function update_config(params)
      categories = params.config.categories
      contentNode = createObject("roSGNode","ContentNode")
      for each category in categories
          node = createObject("roSGNode","category_node")
          node.title = category.title
          node.feed_url = params.config.host + category.feed_url
          node.description = category.description
          contentNode.appendChild(node)
      end for
      m.category_list.content = contentNode
  end function