鸿蒙开发之数据持久化

1.用户首选项

用户首选项（Preference）为应用提供key-value键值型的数据处理能力，支持应对持久化轻量级数据，比如小说app的字体设置背景等

1.1案例

在这里插入图片描述

1.index.ets

import RouterInfo from '../viewmodel/RouterInfo'
import IndexFontSizePanel from '../views/IndexFontSizePanel'
import RouterItem from '../views/RouterItem'
import PreferencesUtil from '../common/util/PreferencesUtil'

const routers: RouterInfo[] = [
  new RouterInfo('pages/ImagePage', '图片查看案例'),
  new RouterInfo('pages/ItemPage', '商品列表案例'),
  new RouterInfo('pages/StatePage', 'Jack和他的女友案例'),
  new RouterInfo('pages/PropPage', '任务列表案例'),
  new RouterInfo('pages/AnimationPage', '小鱼动画案例按钮版'),
  new RouterInfo('pages/AnimationPage2', '小鱼动画案例摇杆版'),
  new RouterInfo('pages/LifeCirclePage', '生命周期案例1'),
  new RouterInfo('pages/TestPage1', '生命周期案例2'),
  new RouterInfo('pages/DocumentListPage', 'UIAbility启动模式案例'),
// new RouterInfo('pages/ShopPage', '查询商铺案例'),
//new RouterInfo('pages/TaskManagePage', '任务列表持久化案例'),
]

@Entry
@Component
struct Index {
  @State message: string = '页面列表'
  @State showPanel: boolean = true
  @Provide fontSize: number = 16

  async aboutToAppear() {
    this.fontSize = await PreferencesUtil.getPreferenceValue('MyPreferences', 'IndexFontSize', 16) as number
  }

  build() {
    Column() {
      // 顶部标题
      this.Title()

      // 导航列表
      this.RouterList()

      // 字体修改面板
      if (this.showPanel) {
        IndexFontSizePanel()
          .transition({
            translate: { y: 115 }
          })
      }
    }
    .width('100%')
    .height('100%')
  }

  @Builder
  Title() {
    Row() {
      Text(this.message)
        .fontSize(50)
        .fontWeight(FontWeight.Bold)
        .height(80)
      Image($r('app.media.ic_public_settings'))
        .width(30)
        .onClick(() => {
          animateTo({ duration: 500, curve: Curve.EaseOut }, () => this.showPanel = !this.showPanel)
        })
    }
    .justifyContent(FlexAlign.SpaceAround)
    .width('100%')
  }

  @Builder
  RouterList() {
    List({ space: 15 }) {
      ForEach(
        routers,
        (router, index) => {
          ListItem() {
            RouterItem({ r: router, i: index + 1 })
          }
        }
      )
    }
    .layoutWeight(1)
    .alignListItem(ListItemAlign.Center)
    .width('100%')
  }
}

2.view/IndexFontSizePanel

import PreferencesUtil from '../common/util/PreferencesUtil'

@Component
export default struct IndexFontSizePanel {
  @Consume fontSize: number
  fontSizLabel: object = {
    14: '小',
    16: '标准',
    18: '大',
    20: '特大',
  }

  build() {
    Column() {
      Text(this.fontSizLabel[this.fontSize]).fontSize(20)
      Row({ space: 5 }) {
        Text('A').fontSize(14).fontWeight(FontWeight.Bold)
        Slider({
          min: 14,
          max: 20,
          step: 2,
          value: this.fontSize
        })
          .showSteps(true)
          .trackThickness(6)
          .layoutWeight(1)
          .onChange(val => {
            // 修改字体大小
            this.fontSize = val
            // 写入Preferences
            PreferencesUtil.putPreferenceValue('MyPreferences', 'IndexFontSize', val)
          })
        Text('A').fontSize(20).fontWeight(FontWeight.Bold)
      }.width('100%')
    }
    .width('100%')
    .padding(15)
    .backgroundColor('#fff1f0f0')
    .borderRadius(20)
  }
}

3.common/util/PreferencesUtil


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

class PreferencesUtil{

  prefMap: Map<string, preferences.Preferences> = new Map()

  async loadPreference(context, name: string){
    try { // 加载preferences
      let pref = await preferences.getPreferences(context, name)
      this.prefMap.set(name, pref)
      console.log('testTag', `加载Preferences[${name}]成功`)
    } catch (e) {
      console.log('testTag', `加载Preferences[${name}]失败`, JSON.stringify(e))
    }
  }

  async putPreferenceValue(name: string, key: string, value: preferences.ValueType){
    if (!this.prefMap.has(name)) {
      console.log('testTag', `Preferences[${name}]尚未初始化！`)
      return
    }
    try {
      let pref = this.prefMap.get(name)
      // 写入数据
      await pref.put(key, value)
      // 刷盘
      await pref.flush()
      console.log('testTag', `保存Preferences[${name}.${key} = ${value}]成功`)
    } catch (e) {
      console.log('testTag', `保存Preferences[${name}.${key} = ${value}]失败`, JSON.stringify(e))
    }
  }

  async getPreferenceValue(name: string, key: string, defaultValue: preferences.ValueType){
    if (!this.prefMap.has(name)) {
      console.log('testTag', `Preferences[${name}]尚未初始化！`)
      return
    }
    try {
      let pref = this.prefMap.get(name)
      // 读数据
      let value = await pref.get(key, defaultValue)
      console.log('testTag', `读取Preferences[${name}.${key} = ${value}]成功`)
      return value
    } catch (e) {
      console.log('testTag', `读取Preferences[${name}.${key} ]失败`, JSON.stringify(e))
    }
  }
}

const preferencesUtil = new PreferencesUtil()

export default preferencesUtil as PreferencesUtil

2.关系型数据库

关系型数据库（RDB）是基于SQLite组件提供的本地数据库，用于管理应用中的结构化数据，例如记账本，备忘录

2.1初始化数据库

2.2增删改数据

2.3查询数据

import relationalStore from '@ohos.data.relationalStore';
import TaskInfo from '../viewmodel/TaskInfo';

class TaskModel {

  private rdbStore: relationalStore.RdbStore
  private tableName: string = 'TASK'

  /**
   * 初始化任务表
   */
  initTaskDB(context){
    // 1.rdb配置
    const config = {
      name: 'MyApplication.db',
      securityLevel: relationalStore.SecurityLevel.S1
    }
    // 2.初始化SQL语句
    const sql = `CREATE TABLE IF NOT EXISTS TASK (
                  ID INTEGER PRIMARY KEY AUTOINCREMENT,
                  NAME TEXT NOT NULL,
                  FINISHED bit
                 )`
    // 3.获取rdb
    relationalStore.getRdbStore(context, config, (err, rdbStore) => {
      if(err){
        console.log('testTag', '获取rdbStore失败！')
        return
      }
      // 执行Sql
      rdbStore.executeSql(sql)
      console.log('testTag', '创建task表成功！')
      // 保存rdbStore
      this.rdbStore = rdbStore
    })
  }

  /**
   * 查询任务列表
   */
  async getTaskList(){
    // 1.构建查询条件
    let predicates = new relationalStore.RdbPredicates(this.tableName)
    // 2.查询
    let result = await this.rdbStore.query(predicates, ['ID', 'NAME', 'FINISHED'])
    // 3.解析查询结果
    // 3.1.定义一个数组，组装最终的查询结果
    let tasks: TaskInfo[] = []
    // 3.2.遍历封装
    while(!result.isAtLastRow){
      // 3.3.指针移动到下一行
      result.goToNextRow()
      // 3.4.获取数据
      let id = result.getLong(result.getColumnIndex('ID'))
      let name = result.getString(result.getColumnIndex('NAME'))
      let finished = result.getLong(result.getColumnIndex('FINISHED'))
      // 3.5.封装到数组
      tasks.push({id, name, finished: !!finished})
    }
    console.log('testTag', '查询到数据：', JSON.stringify(tasks))
    return tasks
  }

  /**
   * 添加一个新的任务
   * @param name 任务名称
   * @returns 任务id
   */
  addTask(name: string): Promise<number>{
    return this.rdbStore.insert(this.tableName, {name, finished: false})
  }

  /**
   * 根据id更新任务状态
   * @param id 任务id
   * @param finished 任务是否完成
   */
  updateTaskStatus(id: number, finished: boolean) {
    // 1.要更新的数据
    let data = {finished}
    // 2.更新的条件
    let predicates = new relationalStore.RdbPredicates(this.tableName)
    predicates.equalTo('ID', id)
    // 3.更新操作
    return this.rdbStore.update(data, predicates)
  }

  /**
   * 根据id删除任务
   * @param id 任务id
   */
  deleteTaskById(id: number){
    // 1.删除的条件
    let predicates = new relationalStore.RdbPredicates(this.tableName)
    predicates.equalTo('ID', id)
    // 2.删除操作
    return this.rdbStore.delete(predicates)
  }
}

let taskModel = new TaskModel();

export default taskModel as TaskModel;