HarmonyOS 如何下载文件，并且下载完毕后，通过代码打开系统文件管理查看该文件

下载网络文件/保存指定路径请参考此demo:

https://gitee.com/harmonyos-cases/cases/tree/master/CommonAppDevelopment/feature/photopickandsave#%E5%9B%BE%E7%89%87%E9%80%89%E6%8B%A9%E5%92%8C%E4%B8%8B%E8%BD%BD%E4%BF%9D%E5%AD%98%E6%A1%88%E4%BE%8B

主动打开系统的文件管理，可参考：

https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/js-apis-inner-ability-want-V5#属性

核心代码demo：

startApp() {
  let context = getContext(this) as common.UIAbilityContext;
  let want: Want = {
    // action: 'ohos.want.action.viewData',
    bundleName: 'com.huawei.hmos.filemanager',
    abilityName: 'MainAbility',
    uri: '',//传对应想要跳转的uri
  };
  context.startAbility(want);
}
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request.downloadFile与documentPicker结合使用示例如下：

//request.ets

import { BusinessError, request } from '@kit.BasicServicesKit';
import fs from '@ohos.file.fs';
import { picker } from '@kit.CoreFileKit';

// 拷贝文件，从沙箱拷贝到公共目录
export function copyFileToCommon(src: string, dst: string) {
  try {
    let file = fs.openSync(src, fs.OpenMode.READ_ONLY);
    let file2 = fs.openSync(dst, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE); //先创建有读写权限的文件，再把不可读写的文件复制过来
    fs.copyFileSync(file.fd, file2.fd);
  } catch (e) {
    console.error("tag copy error")
  }
}

// 下载文件到沙箱目录
export function downloadFile(ctx: Context, fsUri: string, localPath: string) {
  try {
    request.downloadFile(ctx, {
      url: fsUri,
      filePath: localPath // 沙箱路径
    }).then((downloadTask: request.DownloadTask) => {
      downloadTask.on('complete', () => {
        console.info("tag download complete");
      })
    }).catch((err: BusinessError) => {
      console.error("tag invoke download task failed")
    })
  } catch (err) {
    let e = err as BusinessError;
    console.error("tag invoke download file failed, message=" + e.message)
  }
}

export function saveFromDPicker(ctx:Context,localPath: string) {
  const documentSaveOptions = new picker.DocumentSaveOptions(); // 创建文件管理器选项实例
  const documentViewPicker = new picker.DocumentViewPicker(ctx); // 创建文件选择器实例
  documentViewPicker.save(documentSaveOptions).then((documentSaveResult: Array<string>) => {
    let uri = documentSaveResult[0];
    console.info('documentViewPicker.save to file succeed and uris are:' + uri);
    copyFileToCommon(localPath, uri);
  }).catch((err: BusinessError) => {
    console.error(`Invoke documentViewPicker.save failed, code is ${err.code}, message is ${err.message}`);
  })
}
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//index.ets

import { downloadFile, saveFromDPicker } from './request';
import { picker } from '@kit.CoreFileKit';

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';
  @State uri:string = '';

  build() {
    Column() {
      Button('下载文件')
        .onClick(() => {
          console.log('',getContext(this).cacheDir)
          downloadFile(getContext(this), "https://xxx.pdf", getContext(this).cacheDir + "/test.pdf");
        })

      Button('保存文件至管理器')
        .onClick(() => {
          saveFromDPicker(getContext(this),getContext(this).cacheDir + "/test.pdf");
        })
    }.width("100%").height("100%")
  }
}
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