HarmonyOS鸿蒙Next中如何使用fileIo进行文件读写操作？

实现思路：

1. 获取应用沙箱路径并拼接文件路径：

import { fileIo } from '@kit.CoreFileKit';
import { common } from '@kit.AbilityKit';

const context = getContext(this) as common.UIAbilityContext;
const filePath = `${context.filesDir}/data.txt`;

1. 使用 fileIo.open 和 fileIo.write 写入文件：

const file = fileIo.openSync(filePath, fileIo.OpenMode.CREATE | fileIo.OpenMode.READ_WRITE);
fileIo.writeSync(file.fd, 'Hello World');
fileIo.closeSync(file.fd);

1. 使用 fileIo.read 读取文件内容：

const file = fileIo.openSync(filePath, fileIo.OpenMode.READ_ONLY);
const buffer = new ArrayBuffer(4096);
const readLen = fileIo.readSync(file.fd, buffer);
const content = String.fromCharCode(...new Uint8Array(buffer.slice(0, readLen)));
fileIo.closeSync(file.fd);

1. 完整示例代码：

import { fileIo } from '@kit.CoreFileKit';
import { common } from '@kit.AbilityKit';
import { util } from '@kit.ArkTS';

class FileUtil {
  private context: common.UIAbilityContext;

  constructor(context: common.UIAbilityContext) {
    this.context = context;
  }

  getFilePath(fileName: string): string {
    return `${this.context.filesDir}/${fileName}`;
  }

  writeText(fileName: string, content: string): boolean {
    try {
      const filePath = this.getFilePath(fileName);
      const file = fileIo.openSync(filePath, 
        fileIo.OpenMode.CREATE | fileIo.OpenMode.READ_WRITE | fileIo.OpenMode.TRUNC);
      const encoder = new util.TextEncoder();
      const buffer = encoder.encodeInto(content);
      fileIo.writeSync(file.fd, buffer.buffer);
      fileIo.closeSync(file.fd);
      return true;
    } catch (err) {
      console.error(`Write file failed: ${JSON.stringify(err)}`);
      return false;
    }
  }

  readText(fileName: string): string {
    try {
      const filePath = this.getFilePath(fileName);
      if (!fileIo.accessSync(filePath)) {
        return '';
      }
      const file = fileIo.openSync(filePath, fileIo.OpenMode.READ_ONLY);
      const stat = fileIo.statSync(file.fd);
      const buffer = new ArrayBuffer(stat.size);
      fileIo.readSync(file.fd, buffer);
      fileIo.closeSync(file.fd);
      const decoder = new util.TextDecoder();
      return decoder.decodeToString(new Uint8Array(buffer));
    } catch (err) {
      console.error(`Read file failed: ${JSON.stringify(err)}`);
      return '';
    }
  }

  writeJson<T>(fileName: string, data: T): boolean {
    return this.writeText(fileName, JSON.stringify(data));
  }

  readJson<T>(fileName: string, defaultValue: T): T {
    const content = this.readText(fileName);
    if (content) {
      try {
        return JSON.parse(content) as T;
      } catch {
        return defaultValue;
      }
    }
    return defaultValue;
  }

  deleteFile(fileName: string): boolean {
    try {
      const filePath = this.getFilePath(fileName);
      if (fileIo.accessSync(filePath)) {
        fileIo.unlinkSync(filePath);
      }
      return true;
    } catch (err) {
      console.error(`Delete file failed: ${JSON.stringify(err)}`);
      return false;
    }
  }

  fileExists(fileName: string): boolean {
    try {
      return fileIo.accessSync(this.getFilePath(fileName));
    } catch {
      return false;
    }
  }
}

// 使用示例
@Entry
@Component
struct FileOperationPage {
  private fileUtil: FileUtil = new FileUtil(getContext(this) as common.UIAbilityContext);
  @State content: string = '';
  @State savedContent: string = '';

  build() {
    Column({ space: 16 }) {
      Text('文件操作').fontSize(20).fontWeight(FontWeight.Bold)

      TextArea({ placeholder: '输入内容', text: this.content })
        .height(150)
        .onChange((value: string) => {
          this.content = value;
        })

      Row({ space: 12 }) {
        Button('保存').onClick(() => {
          if (this.fileUtil.writeText('note.txt', this.content)) {
            console.info('保存成功');
          }
        })

        Button('读取').onClick(() => {
          this.savedContent = this.fileUtil.readText('note.txt');
        })

        Button('删除').onClick(() => {
          this.fileUtil.deleteFile('note.txt');
          this.savedContent = '';
        })
      }

      if (this.savedContent) {
        Text('已保存内容:').fontSize(14).fontColor('#666')
        Text(this.savedContent)
          .fontSize(14)
          .padding(12)
          .backgroundColor('#F5F5F5')
          .borderRadius(8)
          .width('100%')
      }
    }
    .width('100%')
    .padding(16)
  }
}