开发者学堂的教程：大文件迁移(传输文件大小超过100kb)

@Entry
@Component
struct MailHomePage {

  aboutToAppear() {
    if ((this.isContinuation === CommonConstants.CAN_CONTINUATION) && (this.appendix.length >= 1)) {
      this.readFile();
    }
  }

  build() {
    // ...
  }

  /**
   * Reading file from distributed file systems.
   */
  readFile(): void {
    this.appendix.forEach((item: AppendixBean) => {
      let filePath: string = this.distributedPath + item.fileName;
      let savePath: string = getContext().filesDir + '/' + item.fileName;
      try {
        while (fileIo.accessSync(filePath)) {
          let saveFile = fileIo.openSync(savePath, fileIo.OpenMode.READ_WRITE | fileIo.OpenMode.CREATE);
          let file = fileIo.openSync(filePath, fileIo.OpenMode.READ_WRITE);
          let buf: ArrayBuffer = new ArrayBuffer(CommonConstants.FILE_BUFFER_SIZE);
          let readSize = 0;
          let readLen = fileIo.readSync(file.fd, buf, { offset: readSize });
          while (readLen > 0) {
            readSize += readLen;
            fileIo.writeSync(saveFile.fd, buf);
            readLen = fileIo.readSync(file.fd, buf, { offset: readSize });
          }
          fileIo.closeSync(file);
          fileIo.closeSync(saveFile);
        }
      } catch (error) {
        let err: BusinessError = error as BusinessError;
        Logger.error(`DocumentViewPicker failed with err: ${JSON.stringify(err)}`);
      }
    });
  }

  /**
   * Add appendix from file manager.
   *
   * @param fileType
   */
  documentSelect(fileType: number): void {
    try {
      let DocumentSelectOptions = new picker.DocumentSelectOptions();
      let documentPicker = new picker.DocumentViewPicker();
      documentPicker.select(DocumentSelectOptions).then((DocumentSelectResult: Array<string>) => {
        for (let documentSelectResultElement of DocumentSelectResult) {
          let buf = new ArrayBuffer(CommonConstants.FILE_BUFFER_SIZE);
          let readSize = 0;
          let file = fileIo.openSync(documentSelectResultElement, fileIo.OpenMode.READ_ONLY);
          let readLen = fileIo.readSync(file.fd, buf, { offset: readSize });
          // File name is not supported chinese name.
          let fileName = file.name;
          if (!fileName.endsWith(imageIndex[fileType].fileType) ||
          new RegExp("[\\u4E00-\\u9FA5]|[\\uFE30-\\uFFA0]", "gi").test(fileName)) {
            promptAction.showToast({
              message: $r('app.string.alert_message_chinese')
            })
            return;
          }
          let destination = fileIo.openSync(getContext()
            .filesDir + '/' + fileName, fileIo.OpenMode.READ_WRITE | fileIo.OpenMode.CREATE);
          let destinationDistribute = fileIo.openSync(getContext()
            .distributedFilesDir + '/' + fileName, fileIo.OpenMode.READ_WRITE | fileIo.OpenMode.CREATE);
          while (readLen > 0) {
            readSize += readLen;
            fileIo.writeSync(destination.fd, buf);
            fileIo.writeSync(destinationDistribute.fd, buf);
            console.info(destinationDistribute.path);
            readLen = fileIo.readSync(file.fd, buf, { offset: readSize });
          }
          fileIo.closeSync(file);
          fileIo.closeSync(destination);
          fileIo.closeSync(destinationDistribute);
          this.appendix.push({ iconIndex: fileType, fileName: fileName });
        }
        Logger.info(`DocumentViewPicker.select successfully, DocumentSelectResult uri: ${JSON.stringify(DocumentSelectResult)}`);
      }).catch((err: BusinessError) => {
        Logger.error(`DocumentViewPicker.select failed with err: ${JSON.stringify(err)}`);
      });
    } catch (error) {
      let err: BusinessError = error as BusinessError;
      Logger.error(`DocumentViewPicker failed with err: ${JSON.stringify(err)}`);
    }
  }
}

应用接续开发指导

文档https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/app-continuation-guide

将大文件拆分为多个小块，通过循环分批传输，结合 taskpool 异步处理：

import taskpool from '@kit.TaskPoolKit';
import fs from '@kit.FileKit';
import { BusinessError } from '@ohos.base';

async function copyLargeFileAsync(sourcePath: string, targetPath: string): Promise<void> {
  const CHUNK_SIZE = 1024 * 1024; // 1MB分片
  const stat = fs.statSync(sourcePath);
  const fileSize = stat.size;
  let offset = 0;

  while (offset < fileSize) {
    const readSize = Math.min(CHUNK_SIZE, fileSize - offset);
    const buffer = new ArrayBuffer(readSize);
    const readOptions: fs.ReadOptions = {
      offset: offset,
      length: readSize
    };

    // 分片读取
    fs.readSync(sourcePath, buffer, readOptions);

    // 分片写入（异步任务）
    await taskpool.execute(async () => {
      const writeOptions: fs.WriteOptions = {
        offset: offset,
        encoding: fs.Encoding.UTF8
      };
      try {
        fs.writeSync(targetPath, buffer, writeOptions);
      } catch (error) {
        const err = error as BusinessError;
        console.error(`分片写入失败: ${err.code}, ${err.message}`);
      }
    }, taskpool.Priority.LOW);

    offset += readSize;
  }
}

使用 context 获取分布式文件路径，避免硬编码路径导致的权限错误：

import UIAbility from '@ohos.app.ability.UIAbility';
import { BusinessError } from '@ohos.base';

export default class EntryAbility extends UIAbility {
  onContinue(wantParam: Record<string, Object>) {
    const context = this.context;
    const distributedDir = context.filesDir + '/distributed/'; // 合法分布式目录
    const baseDir = context.filesDir + '/base/'; // 目标目录

    // 启动异步拷贝
    taskpool.execute(() => {
      try {
        copyLargeFileSync(distributedDir + 'largefile.dat', baseDir + 'largefile.dat');
        wantParam['file_transfer_status'] = 'success';
      } catch (error) {
        wantParam['file_transfer_status'] = 'failed';
      }
    }, taskpool.Priority.HIGH);

    return AbilityConstant.OnContinueResult.AGREE;
  }
}