HarmonyOS 鸿蒙Next 文件预览问题

可参考如下代码:

import common from '[@ohos](/user/ohos).app.ability.common';
import fs from '[@ohos](/user/ohos).file.fs';
import { filePreview } from '[@kit](/user/kit).PreviewKit';
import { BusinessError } from '[@kit](/user/kit).BasicServicesKit';
import { fileUri } from '[@kit](/user/kit).CoreFileKit';
import { promptAction } from '[@kit](/user/kit).ArkUI';

[@Entry](/user/Entry)
[@Component](/user/Component)
struct Index {
 [@State](/user/State) message: string = '预览文件';
 [@State](/user/State) src: string = ''

 copyFile() {
   console.log("copyFile!")
   let srcFileDescriptor = getContext().resourceManager.getRawFdSync("6.pdf");

   //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 = getContext().filesDir;

   console.log("path:", pathDir)

   let dstPath = pathDir + "/" + Date.now() + ".pdf";

   this.src = fileUri.getUriFromPath(dstPath)
   console.log("this.src:", this.src)
   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)
   promptAction.showToast({ message: `传入成功` })
 }

 build() {

   Row() {

     Column({ space: 10 }) {

       Button('传到沙箱')

         .onClick(() => {

           this.copyFile()

         })
         .fontSize(50)

       Button(this.message)

         .fontSize(50)

         .fontWeight(FontWeight.Bold)

         .onClick(() => {
           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: '6.pdf',

             uri: this.src,

             mimeType: 'application/pdf' // 文件(夹)的媒体资源类型，如text/plain
           };
           filePreview.openPreview(getContext() as common.UIAbilityContext, fileInfo).then(() => {

             console.info('openPreview success');

           }).catch((err: BusinessError) => {

             console.error('openPreview failed, err = ' + err.message);

           });

         })

     }

     .width('100%')

   }

   .height('100%')

 }
}