在 app.json    文件里面 ：

{
  "pages":[
    "pages/index/index",
    "pages/logs/logs",
    "pages/topic/topic",
    "pages/category/category"
  ],
  "window":{
    "backgroundTextStyle":"light",
    "navigationBarBackgroundColor": "#000",
    "navigationBarTitleText": "大熊图书馆",
    "navigationBarTextStyle":"white"
  },
  "tabBar": {
    "color": "#8c8c8c",//字体颜色
    "selectedColor": "#f4645f", //选中字体颜色
    "backgroundColor": "#fff",//背景颜色
    "list": [{
      "pagePath": "pages/index/index",
      "text": "图书",
      "iconPath":"images/book.png",
      "selectedIconPath":"images/book1.png"
    }, 
    {
      "pagePath": "pages/category/category",      
      "text": "评论",
      "iconPath":"images/book.png",
      "selectedIconPath":"images/book1.png"
    },
    {
      "pagePath": "pages/topic/topic",      
      "text": "我的",
      "iconPath":"images/book.png",
      "selectedIconPath":"images/book1.png"
    }  
    ],
    "position": "bottom"    //写成   top   就在上面
  }  
}