关于如何自定义tabbar，可以参考官方文档(写的比较详细)

源码如下（参考网上代码，按自己理解做了一些优化）仅供参考

index.js

Component({
  data: {
    color: "#515151",
    selectedColor: "#DAA520",
    backgroundColor: "#ffffff",
    list: [
      {
        pagePath: "/pages/index/index",
        text: "流水",
        iconPath: "/img/income.png",
        selectedIconPath: "/img/income-select.png"
      },
      {
        pagePath: "/pages/chart/chart",
        text: "图表",
        iconPath: "/img/chart.png",
        selectedIconPath: "/img/chart-select.png"
      },
      {
        pagePath: "/pages/record/record",
        bulge:true,
        iconPath: "/img/post.png",
        selectedIconPath: "/img/post-select.png"
      },
      {
        pagePath: "/pages/message/message",
        text: "消息",
        iconPath: "/img/message.png",
        selectedIconPath: "/img/message-select.png"
      },
      {
        pagePath: "/pages/home/home",
        text: " 我家",
        iconPath: "/img/home.png",
        selectedIconPath: "/img/home-select.png"
      }
    ]
  },
  attached() {
  },
  methods: {
    switchTab(e) {
      const data = e.currentTarget.dataset
      const url = data.path
      wx.switchTab({url}) 
    }
  }
})

index.json

{
  "component": true
}

index.wxml

<view class="tab-bar">
  <view wx:for="{{list}}" wx:key="index" class="tab-bar-item {{item.bulge?'bulge':''}}" data-path="{{item.pagePath}}" data-index="{{index}}" bindtap="switchTab">
    <view  wx:if="item.bulge" class="tab-bar-bulge"></view>
    <image src="{{selected === index ? item.selectedIconPath : item.iconPath}}"></image>
    <view  wx:if="{{item.text}}" style="color: {{selected === index ? selectedColor : color}}">{{item.text}}</view>
  </view>
</view>

index.wxss

.tab-bar {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  height: 48px;
  background: #FFF;
  display: flex;
  line-height: 1.2;
  padding-bottom: env(safe-area-inset-bottom);
  border-top: 1px solid #e6e6e6;
}

.tab-bar-item {
  flex: 1;
  text-align: center;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
}
.tab-bar-item image {
  width: 27px;
  height: 27px;
}
.bulge {
  background-color: #FFF;
}
.bulge .tab-bar-bulge {
  position: absolute;
  z-index: -1;
  top: -10px;
  width: 80px;
  height: 80px;
  border-radius: 50%;
  border-top: 1px solid #e6e6e6;
  background-color: #FFF;
}
.bulge image{
  position: absolute;
  width: 45px;
  height: 45px;
  top: -12px;
  padding-top: 10px;
}
.tab-bar-item view {
  font-size: 10px;
}

注意：自定义的tabBar需要在页面js里实现

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

欢迎体验

如有问题欢迎评论区交流