How does uniapp implement preloading of several other TabBar pages?

In recent years, mobile applications have become an essential part of people's lives. With the development of mobile applications, more and more applications adopt TabBar design, especially in apps, TabBar has become the main navigation method for many applications. Among them, the Uniapp framework can be said to be the most popular lightweight cross-platform development framework at present. However, many developers will encounter a common problem when using Uniapp to develop TabBar applications: How to preload several other TabBar pages?

During the Uniapp development process, TabBar can be created by configuring the page in pages.json. For example, define the following pages in pages.json:

{
  "pages": [
    {
      "path": "pages/index/index",
      "style": {}
    },
    {
      "path": "pages/category/category",
      "style": {}
    },
    {
      "path": "pages/cart/cart",
      "style": {}
    },
    {
      "path": "pages/me/me",
      "style": {}
    }
  ],
  "tabBar": {
    "color": "#999999",
    "selectedColor": "#000000",
    "backgroundColor": "#ffffff",
    "borderStyle": "black",
    "list": [
      {
        "pagePath": "pages/index/index",
        "text": "首页",
        "iconPath": "static/tabbar/home.png",
        "selectedIconPath": "static/tabbar/home_active.png"
      },
      {
        "pagePath": "pages/category/category",
        "text": "分类",
        "iconPath": "static/tabbar/category.png",
        "selectedIconPath": "static/tabbar/category_active.png"
      },
      {
        "pagePath": "pages/cart/cart",
        "text": "购物车",
        "iconPath": "static/tabbar/cart.png",
        "selectedIconPath": "static/tabbar/cart_active.png"
      },
      {
        "pagePath": "pages/me/me",
        "text": "我的",
        "iconPath": "static/tabbar/me.png",
        "selectedIconPath": "static/tabbar/me_active.png"
      }
    ]
  }
}

In this configuration file, we define 4 pages and create a TabBar. Among them, each page corresponds to a menu item in the TabBar. When we click on different menu items, Uniapp will jump to the corresponding page.

However, in this process, Uniapp will only preload the current page when it is loaded, and will not preload other pages. Therefore, when we switch from one TabBar page to another, the page may load slowly, affecting the user experience. So, how to solve this problem?

Methods to preload other TabBar pages:

In Uniapp, we can preload other TabBar pages by using uni.request. This method can obtain the data of the specified page by sending a GET request and cache the data. When we click the corresponding TabBar menu item, the system will first check whether the data exists in the cache. If it exists in the cache, it will display the data directly. If it does not exist, it will send the request again and cache the data.

In pages.json, add a preload field to define the page URL that needs to be preloaded:

{
  "pages": [
    {
      "path": "pages/index/index",
      "style": {}
    },
    {
      "path": "pages/category/category",
      "style": {},
      "preload": true
    },
    {
      "path": "pages/cart/cart",
      "style": {},
      "preload": true
    },
    {
      "path": "pages/me/me",
      "style": {},
      "preload": true
    }
  ],
  "tabBar": {
    ...
  }
}

In the above configuration file, we add new fields for category, cart and me pages. Added the preload attribute and set it to true. This means that when the App home page is loaded, Uniapp will automatically load these pages and cache them locally.

Next, we call uni.request in App.vue to implement the page preloading function:

<template>
  <div class="app">
    <uni-tab-bar :list="tabBar.list" :color="tabBar.color" :selected-color="tabBar.selectedColor" :background-color="tabBar.backgroundColor" :border-style="tabBar.borderStyle" @change="onTabChange"></uni-tab-bar>
  </div>
</template>

<script>
export default {
  data() {
    return {
      tabBar: uni.getStorageSync('tabBar') || {
        color: '#999999',
        selectedColor: '#000000',
        backgroundColor: '#ffffff',
        borderStyle: 'black',
        list: []
      },
      currentTab: 0
    }
  },
  onLoad() {
    uni.request({
      url: '/pages/me/me',
      method: 'GET',
      success: (res) => {
        uni.setStorageSync('/pages/me/me', res.data)
      }
    })
    uni.request({
      url: '/pages/cart/cart',
      method: 'GET',
      success: (res) => {
        uni.setStorageSync('/pages/cart/cart', res.data)
      }
    })
    uni.request({
      url: '/pages/category/category',
      method: 'GET',
      success: (res) => {
        uni.setStorageSync('/pages/category/category', res.data)
      }
    })
  },
  methods: {
    onTabChange(e) {
      const url = this.tabBar.list[e.index].pagePath
      this.currentTab = e.index
      uni.setStorageSync('currentTab', e.index)
      let pageData = uni.getStorageSync(url)
      if (!pageData) {
        uni.showLoading()
        // 发送请求获取数据
        uni.request({
          url: url,
          method: 'GET',
          success: (res) => {
            uni.hideLoading()
            pageData = res.data
            // 将获取的数据缓存到本地
            uni.setStorageSync(url, pageData)
          }
        })
      }
    }
  }
}
</script>

In the above code, we pass uni in the onLoad method of App.vue .request to obtain the data of category, cart and me pages and cache them locally.

When the TabBar menu item is clicked, we will obtain the corresponding page URL based on the menu item's index and check whether the page has been cached locally. If it is cached, the data is read directly from the cache and the page is rendered; if it is not cached, a GET request is sent to obtain the data and cached locally, and then the page is rendered.

The above is how to preload other TabBar pages in Uniapp. By preloading pages, we can quickly display the corresponding page when the user clicks the TabBar menu item to switch pages, thus improving the user experience.

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