鸿蒙 harmonyos arkts 如何实现本地永久存储

鸿蒙 harmonyos arkts 如何实现本地永久存储呢？官方给我们提供的PersistentStorage持久化数据是没法实现本地存储的

要实现本地永久存储可以使用 @ohos.data.preferences

1、新建common/PreferencesUtil.ets

import preferences from '@ohos.data.preferences';

class PreferencesUtils {
  // 新增数据put
  async set(name: string, key: string, value: preferences.ValueType) {
    try {
      var context: Context = getContext(this)
      const pref = await preferences.getPreferences(context, name)
      // 写入数据
      await pref.put(key, value)
      // 刷盘
      await pref.flush()
      console.log('testTag', `保存preferences[${name}]成功`)
    }

    catch (e) {
      console.log('testTag', `保存preferences[${name}]失败`, JSON.stringify(e));
    }
  }

  // 读取数据get
  async get(name: string, key: string, defaultValue: preferences.ValueType) {
    // 先判断是否存在该名称的键值对

    try {
      var context: Context = getContext(this)
      const pref = await preferences.getPreferences(context, name)
      const value = await pref.get(key, defaultValue)
      console.log('testTag', `读取preferences[${name}.${key}=${value}]成功`)
      return value
    }

    catch (e) {
      console.log('testTag', `读取preferences[${name}]失败`, JSON.stringify(e));
    }
  }

  // 删除数据del
  async delete(name: string, key: string) {
    try {
      var context: Context = getContext(this)
      const pref = await preferences.getPreferences(context, name)
      await pref.delete(key)
      console.log('testTag', `删除preferences[${name}]成功`)
    }
    catch (e) {
      console.log('testTag', `删除preferences[${name}]失败`, JSON.stringify(e));
    }
  }
}

const preferenceUtils = new PreferencesUtils()

export default preferenceUtils

2、使用PreferencesUtils实现永久存储

import { AppBar } from "../../widget/AppBar"
import PreferencesUtils from '../../common/PreferencesUtil'

@Component
export struct Cart {
  @State message: string = ""

  build() {
    Column() {
      AppBar({ title: "购物车" })
      Text(this.message).fontSize(30)

      Button() {
        Text("设置数据").fontSize(14).fontColor(Color.White)
      }.onClick(async () => {

        await PreferencesUtils.set('searchPreference', 'username', '张三')

      }).margin({ top: 20 })
      .padding(20)


      Button() {
        Text("获取").fontSize(14).fontColor(Color.White)
      }.onClick(async () => {

        let msg = await PreferencesUtils.get('searchPreference', 'username', '')

        this.message = msg.toString()
      }).margin({ top: 20 }).padding(20)


      Button() {
        Text("修改").fontSize(14).fontColor(Color.White)
      }.onClick(async () => {

        await PreferencesUtils.set('searchPreference', 'username', '李四')
      }).margin({ top: 20 }).padding(20)


      Button() {
        Text("删除").fontSize(14).fontColor(Color.White)
      }.onClick(async () => {

        await PreferencesUtils.delete("searchPreference","username")
      }).margin({ top: 20 }).padding(20)


    }.height('100%')
    .width("100%")
  }
}