效果如图，使用原生的方式为tabbar加上购物车数量

在此处查看微信文档的自定义tabbar

建议在开发者工具中预览效果

首先在app.json中的tabBar项中加入配置： "custom": true

然后加上 "usingComponents": {}

在加上其他各项配置，这是我的app.json可用以参考

{
  "pages": [
    "pages/index/index",
    "pages/category/index",
    "pages/shoppingCar/index",
    "pages/my/index",
    "pages/goodlist/goodlist",
    "pages/search/index",
    "pages/goodsdetail/index",
    "pages/orderconfirm/index",
    "pages/authorize/index"
  ],
  "window": {
    "backgroundTextStyle": "dark",
    "navigationBarBackgroundColor": "#ff2d4a",
    "navigationBarTitleText": "我的小程序",
    "navigationBarTextStyle": "white",
    "enablePullDownRefresh": true
  },
  "tabBar":{
    "custom": true,
     "color": "#7A7E83",
    "selectedColor": "#ff0000",
    "list": [
      {
        "pagePath": "pages/index/index",
        "text": "首页",
        "iconPath": "./images/[email protected]",
        "selectedIconPath": "./images/[email protected]"
      },
      {
        "pagePath": "pages/category/index",
        "text": "分页",
        "iconPath": "./images/[email protected]",
        "selectedIconPath": "./images/[email protected]"
      },
      {
        "pagePath": "pages/shoppingCar/index",
        "text": "购物车",
        "iconPath": "./images/[email protected]",
        "selectedIconPath": "./images/[email protected]"
      },
      {
        "pagePath": "pages/my/index",
        "text": "我的",
        "iconPath": "./images/[email protected]",
        "selectedIconPath": "./images/[email protected]"
      }
    ]
  },
  "usingComponents": {},
  "style": "v2",
  "sitemapLocation": "sitemap.json"
}

接下来在根目录创建custom-tab-bar文件夹（或者实例中的所有代码考过来）

先完成页面与按钮的对应的配置使得tabbar能够点击跳转

更改custom-tab-bar先index.js中的list配置如下(与app.json对应)

注意注意，此处路径不可写 ./而是要根目录的/否则会报错

Component({
 
  data: {
    selected: 1,
    color: "#7A7E83",
    selectedColor: "#ff0000",
    list: [
      {
        pagePath: "/pages/index/index",
        text: "首页",
        iconPath: "/images/[email protected]",
        selectedIconPath: "/images/[email protected]"
      },
      {
        pagePath: "/pages/category/index",
        text: "分页",
        iconPath: "/images/[email protected]",
        selectedIconPath: "/images/[email protected]"
      },
      {
        pagePath: "/pages/shoppingCar/index",
        text: "购物车",
        iconPath: "/images/[email protected]",
        selectedIconPath: "/images/[email protected]"
      },
      {
        pagePath: "/pages/my/index",
        text: "我的",
        iconPath: "/images/[email protected]",
        selectedIconPath: "/images/[email protected]"
      }
    ],
    shopping_count: (wx.getStorageSync('shopping_car') || [] ).length
  },
  methods: {
    switchTab(e) {
      const data = e.currentTarget.dataset
      const url = data.path
      wx.switchTab({url})
      this.setData({
        selected: data.index
      })
    }
  }
  

})

接下来在每个对应的页面写上如下代码

其中selected为索引值，至此完成自定义tabbar的配置

onShow() {
    if (typeof this.getTabBar === 'function' &&
      this.getTabBar()) {
      this.getTabBar().setData({
        selected: 0
      })
    }
  }

接下来为购物车添加图标

<!--miniprogram/custom-tab-bar/index.wxml-->
<cover-view class="tab-bar">
  <cover-view class="tab-bar-border"></cover-view>
  <cover-view wx:for="{{list}}" wx:key="index" class="tab-bar-item" data-path="{{item.pagePath}}" data-index="{{index}}" bindtap="switchTab">
   
    <cover-image src="{{selected === index ? item.selectedIconPath : item.iconPath}}"></cover-image>
    <cover-view style="color: {{selected === index ? selectedColor : color}}">{{item.text}}</cover-view>
      <!-- 修改这行代码，其中index表示索引（我的购物车在第三个图标，索引为2） -->
     <cover-view class="shoppingCircle" wx:if="{{index === 2}}">{{shopping_count}}</cover-view>
  </cover-view>
</cover-view>

js文件中设置shopping_count变量如下

shopping_count: (wx.getStorageSync('shopping_car') || [] ).length

接着修改css中的内容使得页面呈现预期效果

最后在shoppingcar页面中的onShow中定义函数使得作为操作后点击回来时可以改变显示的数字

if (typeof this.getTabBar === 'function' &&
      this.getTabBar()) {
      this.getTabBar().setData({
        selected: 2
      })
    }