HarmonyOS 文件下载，预览

可参考此demo

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 timeout = 0;
let context = getContext(this) as common.UIAbilityContext;
//新建一个本地应用文件
let cachedir = context.cacheDir;
let file = fs.openSync(cachedir + '/test.txt', fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);
console.log('----------filesDir：' + cachedir)
fs.writeSync(file.fd, 'upload file test');  //以同步方法将数据写入文件
fs.closeSync(file);
// 获取文件的沙箱路径
let pathInSandbox = cachedir + "/test.txt";
console.log('----------pathInSandbox：'+ pathInSandbox)
// 将沙箱路径转换为uri
let uri = fileUri.getUriFromPath(pathInSandbox);
console.log('-----------uri:' + uri);

let uiContext = getContext(this);
filePreview.canPreview(uiContext, uri).then((result) => {    //根据文件的uri判断文件是否可预览 传入支持的文件类型且项目存在时会返回true
  console.info('canPreview. result = ' + result);
}).catch((err: BusinessError) => {
  console.error('canPreview failed, err = ' + err.message);
})
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: 'test.txt',
  uri: uri,
  mimeType: 'text/plain' // 文件(夹)的媒体资源类型，如text/plain
};
@Entry
@Component
struct Index {
  @State message: string = '预览文件';
  build() {
    Row() {
      Column() {
        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%')
  }
}