writeToFile() {
    try {
      let file = fs.openSync(this.filePath, fs.OpenMode.CREATE | fs.OpenMode.READ_WRITE);
      fs.writeSync(file.fd, this.inputText);
      fs.closeSync(file.fd);
      this.outputText = '内容已成功写入文件';
      console.log('写入文件成功');
    } catch (error) {
      console.error(`写入文件失败: ${error.message}`);
      this.outputText = '写入文件失败';
    }
  }

  readFromFile() {
    try {
      if (!fs.accessSync(this.filePath)) {
        this.outputText = '文件不存在';
        return;
      }

      let file = fs.openSync(this.filePath, fs.OpenMode.READ_ONLY);
      let stat = fs.statSync(this.filePath);
      let arrayBuffer = new ArrayBuffer(stat.size);
      fs.readSync(file.fd, arrayBuffer);
      fs.closeSync(file.fd);

      // 使用循环将Uint8Array转换为字符串
      const uint8Array = new Uint8Array(arrayBuffer);
      let result = '';
      for (let i = 0; i < uint8Array.length; i++) {
        result += String.fromCharCode(uint8Array[i]);
      }
      this.outputText = result;
    } catch (error) {
      console.error(`读取文件失败: ${error.message}`);
      this.outputText = '读取文件失败';
    }
  }

1.2 界面代码

build() {
    Column({ space: 20 }) {
      TextInput({ placeholder: '请输入要保存的内容' })
        .width('90%')
        .height(60)
        .onChange((value: string) => {
          this.inputText = value;
        })

      Button('写入文件')
        .width('60%')
        .height(40)
        .onClick(() => {
          this.writeToFile();
        })

      TextInput({ placeholder: '文件内容将显示在这里', text: this.outputText })
        .width('90%')
        .height(60)


      Button('读取文件')
        .width('60%')
        .height(40)
        .onClick(() => {
          this.readFromFile();
        })
    }
    .width('100%')
    .height('100%')
    .justifyContent(FlexAlign.Center)
  }

1.3 \pages\index.ets代码

// MainAbility.ets
import common from '@ohos.app.ability.common';
import fs from '@ohos.file.fs';



@Entry
@Component
struct FileReadWriteExample {
  @State inputText: string = '';
  @State outputText: string = '';
  private context = getContext(this) as common.UIAbilityContext;
  private filePath: string = '';

  aboutToAppear() {
    this.filePath = this.context.filesDir + '/example.txt';

    console.log(`文件路径: ${this.filePath}`);
  }

  writeToFile() {
    try {
      let file = fs.openSync(this.filePath, fs.OpenMode.CREATE | fs.OpenMode.READ_WRITE);
      fs.writeSync(file.fd, this.inputText);
      fs.closeSync(file.fd);
      this.outputText = '内容已成功写入文件';
      console.log('写入文件成功');
    } catch (error) {
      console.error(`写入文件失败: ${error.message}`);
      this.outputText = '写入文件失败';
    }
  }

  readFromFile() {
    try {
      if (!fs.accessSync(this.filePath)) {
        this.outputText = '文件不存在';
        return;
      }

      let file = fs.openSync(this.filePath, fs.OpenMode.READ_ONLY);
      let stat = fs.statSync(this.filePath);
      let arrayBuffer = new ArrayBuffer(stat.size);
      fs.readSync(file.fd, arrayBuffer);
      fs.closeSync(file.fd);

      // 使用循环将Uint8Array转换为字符串
      const uint8Array = new Uint8Array(arrayBuffer);
      let result = '';
      for (let i = 0; i < uint8Array.length; i++) {
        result += String.fromCharCode(uint8Array[i]);
      }
      this.outputText = result;
    } catch (error) {
      console.error(`读取文件失败: ${error.message}`);
      this.outputText = '读取文件失败';
    }
  }

  build() {
    Column({ space: 20 }) {
      TextInput({ placeholder: '请输入要保存的内容' })
        .width('90%')
        .height(60)
        .onChange((value: string) => {
          this.inputText = value;
        })

      Button('写入文件')
        .width('60%')
        .height(40)
        .onClick(() => {
          this.writeToFile();
        })

      TextInput({ placeholder: '文件内容将显示在这里', text: this.outputText })
        .width('90%')
        .height(60)


      Button('读取文件')
        .width('60%')
        .height(40)
        .onClick(() => {
          this.readFromFile();
        })
    }
    .width('100%')
    .height('100%')
    .justifyContent(FlexAlign.Center)
  }
}

1.4 演示

二、首选项读写

2.1 页面显示代码index.ets，实现显示3个按钮。

// index.ets
@Entry
@Component
struct Index {
  build() {
    Column() {
      Button('Button 1')
        .margin({ top: 10, bottom: 10 })
        .onClick(() => {
          // 通过全局对象调用Ability方法
          if (globalThis.entryAbility?.btn1) {
            globalThis.entryAbility.btn1();
          }
      })
        .width('100%')
      Row()
      Button('Button 2')
        .margin({ top: 10, bottom: 10 })
        .onClick(() => {
          if (globalThis.entryAbility?.btn2) {
            globalThis.entryAbility.btn2();
          }
        })
        .width('100%')

      Button('Button 3')
        .margin({ top: 10, bottom: 10 })
        .onClick(() => {
          if (globalThis.entryAbility?.btn3) {
            globalThis.entryAbility.btn3();
          }
        })
        .width('100%')
    }
    .width('100%')
    .height('100%')
  }
}

2.2 UIAbility的代码EntryAbility.ets,功能包括

初始化Preferences数据存储

提供三个按钮操作：

btn1(): 写入字符串、二进制数据和数字到Preferences

btn2(): 从Preferences读取并显示存储的数据

btn3(): 删除Preferences中的数据

Preferences操作
代码中提供了完整的Preferences CRUD操作：

初始化：initPreferences()异步方法

写入数据：btn1()使用putSync()同步写入三种类型数据、字符串、二进制数据(Uint8Array)、数字

读取数据：btn2()使用getSync()同步读取数据、使用TextDecoder解码二进制数据

删除数据：btn3()使用deleteSync()同步删除数据

Preferences同步/异步操作：

初始化使用异步getPreferences()

数据操作使用同步方法(putSync, getSync, deleteSync)

写入后调用flushSync()确保数据持久化

以下为代码

import { AbilityConstant, ConfigurationConstant, UIAbility, Want } from '@kit.AbilityKit';
import { hilog } from '@kit.PerformanceAnalysisKit';
import { window } from '@kit.ArkUI';


import { BusinessError } from '@kit.BasicServicesKit';

import { preferences } from '@kit.ArkData';
import { util } from '@kit.ArkTS';


const DOMAIN = 0x0000;
let dataPreferences: preferences.Preferences | null = null;

export default class EntryAbility extends UIAbility {
  // 初始化Preferences
  async initPreferences(): Promise<void> {
    try {
      let options: preferences.Options = { name: 'myStore' };
      dataPreferences = await preferences.getPreferences(this.context, options);
    } catch (err) {
      hilog.error(DOMAIN, 'testTag', 'Failed to get preferences. Cause: %{public}s', JSON.stringify(err));
    }
  }

  // 按钮1：写入数据
  btn1(): void {
    if (!dataPreferences) {
      console.error('click btn1 Preferences not initialized');
      return;
    }

    try {
      // 写入字符串
      dataPreferences.putSync('string_key', 'Hello ArkTS');

      // 写入Uint8Array
      let encoder = new util.TextEncoder();
      let uInt8Array = encoder.encodeInto("你好，ArkTS");
      dataPreferences.putSync('binary_key', uInt8Array);

      // 写入数字
      dataPreferences.putSync('number_key', 123);

      dataPreferences.flushSync();

      console.info('click btn1 Preferences Data written successfully');
    } catch (err) {
      console.error('click btn1 Preferences Failed to write data: ' + JSON.stringify(err));
    }
  }

  // 按钮2：读取数据
  btn2(): void {
    if (!dataPreferences) {
      console.error('click btn2 Preferences not initialized');
      return;
    }

    try {
      // 读取字符串
      let stringVal = dataPreferences.getSync('string_key', 'default');
      console.info('click btn2 Preferences String value: ' + stringVal);

      // 读取二进制数据
      let binaryVal = dataPreferences.getSync('binary_key', new Uint8Array(0));
      let decoder = new util.TextDecoder('utf-8');
      let decodedStr = decoder.decode(binaryVal as Uint8Array);
      console.info('click btn2 Preferences Binary value: ' + decodedStr);

      // 读取数字
      let numberVal = dataPreferences.getSync('number_key', 0);
      console.info('click btn2 Preferences Number value: ' + numberVal);
    } catch (err) {
      console.error('click btn2 Preferences Failed to read data: ' + JSON.stringify(err));
    }
  }

  // 按钮3：删除数据
  btn3(): void {
    if (!dataPreferences) {
      console.error('click btn3 Preferences not initialized');
      return;
    }

    try {
      dataPreferences.deleteSync('string_key');
      dataPreferences.deleteSync('binary_key');
      dataPreferences.deleteSync('number_key');
      console.info('click btn3 Preferences Data deleted successfully');
    } catch (err) {
      console.error('click btn3 Preferences Failed to delete data: ' + JSON.stringify(err));
    }
  }

  onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
    this.context.getApplicationContext().setColorMode(ConfigurationConstant.ColorMode.COLOR_MODE_NOT_SET);
    hilog.info(DOMAIN, 'testTag', '%{public}s', 'Ability onCreate');

    globalThis.abilityContext = this.context;
    globalThis.entryAbility = this;

    // 初始化Preferences
    this.initPreferences();
  }

  onWindowStageCreate(windowStage: window.WindowStage): void {
    // Main window is created, set main page for this ability
    hilog.info(DOMAIN, 'testTag', '%{public}s', 'Ability onWindowStageCreate');

    windowStage.loadContent('pages/Index', (err) => {
      if (err.code) {
        hilog.error(DOMAIN, 'testTag', 'Failed to load the content. Cause: %{public}s', JSON.stringify(err));
        return;
      }
      hilog.info(DOMAIN, 'testTag', 'Succeeded in loading the content.');
    });

    /*
    let options: preferences.Options = { name: 'myStore' };
    dataPreferences = preferences.getPreferencesSync(this.context, options);


    if (dataPreferences.hasSync('startup')) {
      console.info("The key 'startup' is contained.");
    } else {
      console.info("The key 'startup' does not contain.");
      // 此处以此键值对不存在时写入数据为例
      dataPreferences.putSync('startup', 'auto');
      // 当字符串有特殊字符时，需要将字符串转为Uint8Array类型再存储，长度均不超过16 * 1024 * 1024个字节。
      //let uInt8Array1 = new util.TextEncoder().encodeInto("~！@#￥%……&*（）——+？");


      let encoder: util.TextEncoder = new util.TextEncoder();
      let uInt8Array1: Uint8Array = encoder.encodeInto("你好，ArkTS"); // 或 encode()

      dataPreferences.putSync('uInt8', uInt8Array1);
    }

    let val = dataPreferences.getSync('startup', 'default');
    console.info("The 'startup' value is " + val);
    // 当获取的值为带有特殊字符的字符串时，需要将获取到的Uint8Array转换为字符串
    let uInt8Array2 : preferences.ValueType = dataPreferences.getSync('uInt8', new Uint8Array(0));

    let textDecoder = util.TextDecoder.create('utf-8');
    val = textDecoder.decodeToString(uInt8Array2 as Uint8Array);




    console.info("The 'uInt8' value is " + val);

    */
  }

  onWindowStageDestroy(): void {
    // Main window is destroyed, release UI related resources
    hilog.info(DOMAIN, 'testTag', '%{public}s', 'Ability onWindowStageDestroy');
  }

  onForeground(): void {
    // Ability has brought to foreground
    hilog.info(DOMAIN, 'testTag', '%{public}s', 'Ability onForeground');
  }

  onBackground(): void {
    // Ability has back to background
    hilog.info(DOMAIN, 'testTag', '%{public}s', 'Ability onBackground');
  }
}

2.3 测试效果如下，测试了写入，读出，删除。删除后再读出则为空。