微信小程序底部导航中间水滴凹槽

以下是微信小程序底部导航中间水滴凹槽的实现方法：
1. 在app.json文件中设置tabBar的样式，将中间按钮的位置留出来，例如：

"tabBar": {
  "color": "#999999",
  "selectedColor": "#1296db",
  "backgroundColor": "#ffffff",
  "borderStyle": "black",
  "list": [
    {
      "pagePath": "pages/index/index",
      "text": "首页",
      "iconPath": "images/tabbar/home.png",
      "selectedIconPath": "images/tabbar/home_active.png"
    },
    {
      "pagePath": "pages/mine/mine",
      "text": "我的",
      "iconPath": "images/tabbar/mine.png",
      "selectedIconPath": "images/tabbar/mine_active.png"
    },
    {
      "pagePath": "pages/center/center",
      "text": "",
      "iconPath": "images/tabbar/center.png",
      "selectedIconPath": "images/tabbar/center_active.png"
    },
    {
      "pagePath": "pages/cart/cart",
      "text": "购物车",
      "iconPath": "images/tabbar/cart.png",
      "selectedIconPath": "images/tabbar/cart_active.png"
    },
    {
      "pagePath": "pages/category/category",
      "text": "分类",
      "iconPath": "images/tabbar/category.png",
      "selectedIconPath": "images/tabbar/category_active.png"
    }
  ]
}

2. 在TabBar组件中添加中间按钮的样式，例如：

.tabbar-center {
  position: fixed;
  left: 50%;
  bottom: 0;
  transform: translateX(-50%);
  z-index: 999;
  width: 60rpx;
  height: 60rpx;
  border-radius: 50%;
  background-color: #1296db;
  box-shadow: 0 2rpx 4rpx rgba(0, 0, 0, 0.15);
}

3. 在TabBar组件中添加中间按钮的点击事件，例如：

methods: {
  onCenterClick() {
    wx.navigateTo({
      url: '/pages/center/center'
    })
  }
}

4. 在TabBar组件中添加中间按钮的图片和文字，例如：

<view class="tabbar-center" @tap="onCenterClick">
  <image src="/static/images/tabbar/center.png" class="tabbar-center-icon"></image>
  <text class="tabbar-center-text">中心</text>
</view>