UniApp is a cross-platform development framework based on Vue.js that can be used to develop various applications, including web applications, mobile applications and desktop applications. In actual development, we often face some problems, such as unstable network, offline user access, etc. In order to improve user experience, we need to implement offline caching and data persistence functions in UniApp. This article will introduce the design and development methods of offline caching and data persistence in UniApp, and give corresponding code examples.

1. Offline cache design and development method

Offline cache refers to caching network requested data locally, and users can continue to access cached data without a network connection. In UniApp, you can use uni.setStorageSync and uni.getStorageSync to implement offline caching function.

First, we need to define a tool function to determine whether the cache has expired:

function isCacheExpired(cacheTime) {
  if (!cacheTime) {
    return true;
  }
  const currentTime = new Date().getTime();
  const expireTime = new Date(cacheTime).getTime() + 24 * 60 * 60 * 1000; // 緩存時(shí)間為一天
  return currentTime > expireTime;
}

Next, when initiating a network request, we can first determine whether the cache exists. If it exists and has not expires, the cached data will be used directly. Otherwise, send a network request and cache the returned data.

import { isCacheExpired } from '@/utils'

async function fetchData(api, dataKey, cacheKey) {
  const cache = uni.getStorageInfoSync(cacheKey);
  if (cache && !isCacheExpired(cache.time)) {
    return uni.getStorageSync(cacheKey);
  }else{
    const res = await uni.request({
      url: api,
      method: 'GET',
      data: dataKey,
    });
    const data = res.data;
    uni.setStorageSync(cacheKey, { data, time: new Date() });
    return data;
  }
}

When using the fetchData function, we need to pass in the api, dataKey and cacheKey parameters. Among them, api is the interface address of the network request, dataKey is the request parameter, and cacheKey is the cached key value.

2. Data persistence design and development method

Data persistence refers to saving the data in the application locally, so that the data can still be read the next time the application is opened. In UniApp, you can use uni.setStorageSync and uni.getStorageSync to implement the data persistence function.

First, we need to define a global store object to save the data that needs to be persisted:

const store = {
  state: {
    userInfo: null,
    token: null,
  },
  setUserInfo(userInfo) {
    this.state.userInfo = userInfo;
    uni.setStorageSync('userInfo', userInfo);
  },
  setToken(token) {
    this.state.token = token;
    uni.setStorageSync('token', token);
  },
  init() {
    this.state.userInfo = uni.getStorageSync('userInfo');
    this.state.token = uni.getStorageSync('token');
  },
};
store.init();
export default store;

When the application starts, we need to call the init function of the store to retrieve data from the local cache. Read the saved data and initialize the store object. This way, even if the app is closed and reopened, the data can still be read correctly.

When the application needs to update the data in the store, we not only need to update the state attribute of the store object, but also need to save the updated data to the local cache:

import store from '@/store'

function setUserInfo(userInfo) {
  store.setUserInfo(userInfo);
  // 其他邏輯
}

function setToken(token) {
  store.setToken(token);
  // 其他邏輯
}

In the above code In the fragment, the setUserInfo function and setToken function respectively update the state attribute of the store object, and call the uni.setStorageSync function to save the data to the local cache. This way, the next time you open the app, the data will be read from the local cache.

In summary, the design and development methods for implementing offline caching and data persistence functions in UniApp are as described above. By properly using the uni.setStorageSync and uni.getStorageSync functions, we can easily implement offline caching and data persistence functions and improve the user experience of the application. Of course, in actual development, some adjustments and optimizations need to be made based on specific business scenarios. I hope this article can provide some help to everyone in researching and using UniApp.

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