HarmonyOS 文件下载并且同步进行预览

常见的office文档，本地沙箱路径pdf、doc、docx、xls、xlsx、ppt、pptx已经可以预览。

示例参考：

import common from '@ohos.app.ability.common';
import fs from '@ohos.file.fs';
import { filePreview } from '@kit.PreviewKit';
import { BusinessError } from '@kit.BasicServicesKit';
import fileUri from '@ohos.file.fileuri';

let context = getContext(this) as common.UIAbilityContext;
let uiContext = getContext(this);

let fileInfo: filePreview.PreviewInfo = {
  // 文件预览信息，包含了文件标题名、uri以及文件类型（mimeType）
  title: '1.xls',
  // title: '蓝牙ble 模式的demo使用说明1.pdf',
  // uri: 'file://com.lvhui.myapplication/data/storage/el2/base/haps/entry/files/蓝牙ble 模式的demo使用说明1.pdf',
  uri: 'file://com.xxx.myapplication/data/storage/el2/base/haps/entry/files/1.xls',
  // mimeType: 'application/pdf' // 文件(夹)的媒体资源类型，如text/plain
  mimeType: 'application/vnd.ms-excel' // 文件(夹)的媒体资源类型，如text/plain
};

function copyFile() {
  console.log("copyFile!")
  // let srcFileDescriptor = context.resourceManager.getRawFdSync('蓝牙ble 模式的demo使用说明1.pdf');
  let srcFileDescriptor = context.resourceManager.getRawFdSync('1.xls');
  //这里填rawfile文件夹下的文件名（包括后缀）
  let stat = fs.statSync(srcFileDescriptor.fd)
  console.log(`stat isFile:${stat.isFile()}`);
  // 通过UIAbilityContext获取沙箱地址filesDir，以Stage模型为例
  let pathDir = context.filesDir;
  console.log("path:", pathDir)
  // let dstPath = pathDir + "/蓝牙ble 模式的demo使用说明1.pdf";
  let dstPath = pathDir + "/1.xls";
  let dest = fs.openSync(dstPath, fs.OpenMode.CREATE | fs.OpenMode.READ_WRITE)
  let bufsize = 4096
  let buf = new ArrayBuffer(bufsize)
  let off = 0, len = 0, readedLen = 0
  while (len = fs.readSync(srcFileDescriptor.fd, buf, { offset: srcFileDescriptor.offset + off, length: bufsize })) {
    readedLen += len
    fs.writeSync(dest.fd, buf, { offset: off, length: len })
    off = off + len
    if ((srcFileDescriptor.length - readedLen) < bufsize) {
      bufsize = srcFileDescriptor.length - readedLen
    }
  }
  fs.close(dest.fd)
}

@Entry
@Component
struct Index {
  @State message: string = '预览文件';

  build() {
    Row() {
      Column() {
        Button('传到沙箱')
          .onClick(() => {
            copyFile()
          })
        Button(this.message)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
          .onClick(() => {
            filePreview.openPreview(uiContext, fileInfo).then(() => {
              console.info('openPreview success');
            }).catch((err: BusinessError) => {
              console.error('openPreview failed, err = ' + err.message);
            });
          })
      }
      .width('100%')
    }
    .height('100%')
  }
}