分析：

1. 选中时显示背景和文字，图标变换为选中状态的图标
2. 默认状态下，进入小程序显示的是中间的 “地图”
3. 选中 “预约”时，隐藏tabbar ，且导航栏显示 返回 按钮，点击返回 “地图”

整体效果

整体目录

设置 app.json

在 app.json中 配置tabbar 中的 “custom”: true

{
  "pages": [
    "custom-pages/custom-active/index",
    "custom-pages/custom-order/index",
    "custom-pages/custom-my/index"
  ],
  "entryPagePath":  "custom-pages/custom-active/index",
  "window": {
    "backgroundTextStyle": "light",
    "navigationBarBackgroundColor": "#fff",
    "navigationBarTitleText": "自定义tabbar",
    "navigationBarTextStyle": "black"   
  },
  "tabBar": {
    "custom": true,
    "list": [
      {
        "pagePath": "custom-pages/custom-my/index",
        "text": "我的",
        "iconPath": "/images/tabbar/my.png"
      },
      {
        "pagePath": "custom-pages/custom-active/index",
        "text": "活动"
      },
      {
        "pagePath": "custom-pages/custom-order/index",
        "text": "预约"
      }
    ]
  },
  "usingComponents": {},
}

在项目根目录下，添加 custom-tab-bar

custom-tab-bar为component

编写 tabBar 代码

用自定义组件的方式编写即可，该自定义组件完全接管 tabBar 的渲染。另外，自定义组件新增 getTabBar 接口，可获取当前页面下的自定义 tabBar 组件实例
在根目录下新建文件夹名为 custom-pages ，存放自定义tabbar的页面
custom-pages
-> custom-active
-> custom-my
-> custom-order

custom-tab-bar代码

Component({
  data: {
    // tabbar 的列表 
    tabbarLists:[
      {
        pagePath: "/custom-pages/custom-my/index",
        text: "我的",
        iconPath: "/images/tabbar/my.png",
        selectedIconPath: "/images/tabbar/my_active.png"
      },
      {
        pagePath: "/custom-pages/custom-active/index",
        text: "地图",
        iconPath: "/images/tabbar/map.png",
        selectedIconPath: "/images/tabbar/map_active.png"
      },
      {
        pagePath: "/custom-pages/custom-order/index",
        text: "预约",
        iconPath: "/images/tabbar/order.png",
        selectedIconPath: "/images/tabbar/order_active.png"
      }
    ],
    active:null, //设为数字，会产生tabbar闪烁
    isShow:true //控制显示隐藏tabbar 
  },
  methods: {
    switchTab(e){
      const { index,url } = e.currentTarget.dataset;
      wx.switchTab({url})
    }
  }
})

<view class="tab-bar" wx:if="{{isShow}}">
  <block wx:for="{{tabbarLists}}" wx:key="item">
    <view class="tab-bar-item" 
      data-index="{{index}}" 
      data-url="{{item.pagePath}}"
      bindtap="switchTab"
      >     
      <image class="icon" 
        src="{{active == index?item.selectedIconPath:item.iconPath}}"></image>
      <view class="text {{active == index?'active':''}}">{{item.text}}</view>

    	<!-- 设置选中状态下的背景 -->
      <view wx:if="{{active == index}}" class="bg-item"></view>
    </view>
  </block>
</view>

.tab-bar{
  height: 48px;
  background-color: #ffffff;
  display: flex;
  border-top: 1rpx solid #f9f9f9;
  box-shadow:  0 0 5rpx #f8f8f8;
}
.tab-bar-item{
  display: flex;
  flex: 1;
  justify-content: center;
  align-items: center;
  position: relative;
}
.icon{
  width: 27px;
  height: 27px;
}
.text{
  font-size: 26rpx;
  padding: 0 5rpx;
  letter-spacing: 0.1rem;
  display: none;
}
.active{
  color: #10B981;
  display: block;
  font-weight: 800;
}
.bg-item{
  position: absolute;
  width: 80%;
  top: 15rpx;
  bottom: 15rpx;
  border-radius: 40rpx;
  background-color:rgba(52, 211, 153,0.15);
}

tabbar的page页

一共3个tabbar的page页：custom-active、custom-my、custom-order

custom-active 页 核心代码

Page({
  onShow() {
    if (typeof this.getTabBar === 'function' &&
    this.getTabBar()) {
    this.getTabBar().setData({
      active: 1
    })
  }
  }
})

custom-my 核心代码

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

custom-order

• 该page页要隐藏 tabbar ，所以要将 isShow设置为false;
• 使用 custom-navigator 自定义组件 显示 头部导航

<!-- 使用自定义组件导航头 -->
<custom-navigator 
  title="{{title}}">
</custom-navigator> 

Page({
  data: {
    title:"预约"
  },
  onShow() {
    if (typeof this.getTabBar === 'function' &&
        this.getTabBar()) {
        this.getTabBar().setData({
          active: 2,
          isShow:false
        })
    }
  }
})

{
  "usingComponents": {
    "custom-navigator":"/components/custom-navigator/custom-navigator"
  },
  "navigationStyle": "custom"
}

custom-navigator 自定义组件

<view class="status"></view>
<view class="navigator">
  <view class="icon">
    <image  
      bindtap="gobackTap
      class="icon-image" src="/images/back.png"></image>
  </view>
  <view class="text">{{title}}</view>
  <view class="right"></view>
</view>

.status{
  height: 20px;
}
.navigator{
  height: 44px;
  background-color: #ffffff; 
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: center;
}
.icon{
  width: 40px;
  height: inherit;
  display: flex;
  align-items: center;
  justify-content: center;
  
}
.icon-image{
  width: 27rpx;
  height: 27rpx;
  border: 1rpx solid #cccccc;
  padding: 8rpx;
  border-radius: 20rpx;
}
.text{
  color: #333333;
  flex: 1;
  text-align: center;
  font-size: 28rpx;
}
.right{
  color: #333333;
  width: 40px;
}

Component({
  properties: {
    title:{
      type:String,
      value:"标题"
    }
  },
  methods: {
    gobackTap(e){
      wx.switchTab({
        url: '/custom-pages/custom-active/index',
      })
    }
  }
})