一、官方文档

二、在app.json里面添加tabBar配置

"pages":[
    "pages/index/index",
    "pages/logs/logs",
    "pages/goods/index"
  ],
 "tabBar": {
    "custom": true,
    "color": "#000000",
    "selectedColor": "#000000",
    "backgroundColor": "#000000",
    "list": [{
      "pagePath": "pages/index/index",
      "text": "首页"
    }, {
      "pagePath": "pages/goods/index",
      "text": "商品"
    }]
  }

三、在custom-tab-bar添加配置

1. 在custom-tab-bar创建如下目录

custom-tab-bar/index.js
custom-tab-bar/index.json
custom-tab-bar/index.wxml
custom-tab-bar/index.wxss

2.给index.wxml添加tabBar的结构代码

<!--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>
  </cover-view>
</cover-view>

3. 给index.js 添加数据配置 和 事件方法

Component({
  data: {
    selected: 0,
    color: "#7A7E83",
    selectedColor: "#3cc51f",
    list: [{
      pagePath: "/pages/index/index",
      iconPath: "/image/home2_icon.png",
      selectedIconPath: "/image/home1_icon.png",
      text: "首页"
    }, {
      pagePath: "/pages/goods/index",
      iconPath: "/image/readTrain2_icon.png",
      selectedIconPath: "/image/readTrain1_icon.png",
      text: "商品"
    }]
  },
  attached() {
  },
  methods: {
    switchTab(e) {
      console.log("执行跳转",e);
      const data = e.currentTarget.dataset
      const url = data.path
      wx.switchTab({url})
      this.setData({
        selected: data.index
      })
    }
  }
})

4. 给index.wxss 添加样式

/* custom-tab-bar/index.wxss */
.tab-bar {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  height: 48px;
  background: white;
  display: flex;
  padding-bottom: env(safe-area-inset-bottom);
}

.tab-bar-border {
  background-color: rgba(0, 0, 0, 0.33);
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 1px;
  transform: scaleY(0.5);
}

.tab-bar-item {
  flex: 1;
  text-align: center;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
}

.tab-bar-item cover-image {
  width: 27px;
  height: 27px;
}

.tab-bar-item cover-view {
  font-size: 10px;
}

此时，通过点击切换页面，就可以实现

=》如果在选择点击切换按钮时，页面没根据tabBar进行切换，问题很可能能在custom-tab-bar目录的index.js 的list数据配置的页面路径，一定要/开头，如/pages/goods/index，这才能找到页面。

四、tabbar图标切换 要点击两次才能有选中状态

在`/pages/index目录的index.js文件，的onShow生命周期方法，添加如下代码

onShow() {
    if (typeof this.getTabBar === function &&
      this.getTabBar()) {
      this.getTabBar().setData({
        //唯一标识（其它设置不同的整数）  
        selected: 0
      })
    }
  },

在pages/goods/目录的index.js文件，的onShow生命周期方法，添加如下代码，

onShow() {
    if (typeof this.getTabBar === function &&
      this.getTabBar()) {
      this.getTabBar().setData({
        //唯一标识（其它设置不同的整数）  
        selected: 1
      })
    }
  },

注意：预览时，提示登陆的用户不是小程序的开发者，可添加appid。