HarmonyOS鸿蒙Next中Preferences数据持久化存储怎么使用？数据写入后读取为空

写入数据后没有调用 flush() 方法！ Preferences 的数据修改是在内存中进行的，必须调用 flush() 才会写入磁盘。

1. 正确的写入方式

import { preferences } from '@kit.ArkData'

// 写入数据 - 必须调用 flush()
const pref = await preferences.getPreferences(context, 'settings')
await pref.put('username', '张三')
await pref.put('age', 25)
await pref.flush()  // 关键！必须调用才会持久化

2. 完整的数据存储服务封装

import { preferences } from '@kit.ArkData'
import { common } from '@kit.AbilityKit'

class DataStore {
  private static instance: DataStore
  private dataStore: preferences.Preferences | null = null
  private context: common.UIAbilityContext | null = null
  
  static getInstance(): DataStore {
    if (!DataStore.instance) {
      DataStore.instance = new DataStore()
    }
    return DataStore.instance
  }
  
  // 初始化（在EntryAbility中调用）
  async init(context: common.UIAbilityContext): Promise<void> {
    this.context = context
    this.dataStore = await preferences.getPreferences(context, 'app_data')
  }
  
  // 存储字符串
  async putString(key: string, value: string): Promise<void> {
    await this.dataStore?.put(key, value)
    await this.dataStore?.flush()  // 必须调用！
  }
  
  // 读取字符串
  async getString(key: string, defaultValue: string = ''): Promise<string> {
    return await this.dataStore?.get(key, defaultValue) as string
  }
  
  // 存储数字
  async putNumber(key: string, value: number): Promise<void> {
    await this.dataStore?.put(key, value)
    await this.dataStore?.flush()
  }
  
  // 读取数字
  async getNumber(key: string, defaultValue: number = 0): Promise<number> {
    return await this.dataStore?.get(key, defaultValue) as number
  }
  
  // 存储布尔值
  async putBoolean(key: string, value: boolean): Promise<void> {
    await this.dataStore?.put(key, value)
    await this.dataStore?.flush()
  }
  
  // 读取布尔值
  async getBoolean(key: string, defaultValue: boolean = false): Promise<boolean> {
    return await this.dataStore?.get(key, defaultValue) as boolean
  }
  
  // 存储对象（JSON序列化）
  async putObject<T>(key: string, value: T): Promise<void> {
    const json = JSON.stringify(value)
    await this.dataStore?.put(key, json)
    await this.dataStore?.flush()
  }
  
  // 读取对象
  async getObject<T>(key: string, defaultValue: T): Promise<T> {
    const json = await this.dataStore?.get(key, '') as string
    if (json) {
      try {
        return JSON.parse(json) as T
      } catch (e) {
        return defaultValue
      }
    }
    return defaultValue
  }
  
  // 删除数据
  async delete(key: string): Promise<void> {
    await this.dataStore?.delete(key)
    await this.dataStore?.flush()
  }
  
  // 清空所有数据
  async clear(): Promise<void> {
    await this.dataStore?.clear()
    await this.dataStore?.flush()
  }
  
  // 检查key是否存在
  async has(key: string): Promise<boolean> {
    return await this.dataStore?.has(key) ?? false
  }
}

export const dataStore = DataStore.getInstance()

3. 在EntryAbility中初始化

import { dataStore } from '../utils/DataStore'

export default class EntryAbility extends UIAbility {
  async onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): Promise<void> {
    // 初始化数据存储
    await dataStore.init(this.context)
  }
}

4. 在页面中使用

import { dataStore } from '../utils/DataStore'

@Entry
@Component
struct SettingsPage {
  @State username: string = ''
  @State darkMode: boolean = false
  
  async aboutToAppear(): Promise<void> {
    // 读取保存的设置
    this.username = await dataStore.getString('username', '未设置')
    this.darkMode = await dataStore.getBoolean('darkMode', false)
  }
  
  build() {
    Column({ space: 16 }) {
      // 用户名设置
      Row() {
        Text('用户名')
        TextInput({ text: this.username })
          .onChange(async (value) => {
            this.username = value
            await dataStore.putString('username', value)
          })
      }
      
      // 深色模式开关
      Row() {
        Text('深色模式')
        Toggle({ isOn: this.darkMode })
          .onChange(async (isOn) => {
            this.darkMode = isOn
            await dataStore.putBoolean('darkMode', isOn)
          })
      }
    }
    .padding(16)
  }
}

5. 存储复杂对象

interface UserSettings {
  theme: string
  fontSize: number
  notifications: boolean
  language: string
}

// 存储对象
const settings: UserSettings = {
  theme: 'dark',
  fontSize: 16,
  notifications: true,
  language: 'zh-CN'
}
await dataStore.putObject('userSettings', settings)

// 读取对象
const savedSettings = await dataStore.getObject<UserSettings>('userSettings', {
  theme: 'light',
  fontSize: 14,
  notifications: false,
  language: 'en'
})