downloadManager = DownloadService.getDownloadManager(context.getApplicationContext());

//create download info set download uri and save path.
File targetFile = new File(getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS), "a.apk");
final DownloadInfo downloadInfo = new DownloadInfo.Builder().setUrl("http://example.com/a.apk")
    .setPath(targetFile.getAbsolutePath())
    .build();

//set download callback.
downloadInfo.setDownloadListener(new DownloadListener() {

  @Override
  public void onStart() {
      tv_download_info.setText("Prepare downloading");
  }

  @Override
  public void onWaited() {
      tv_download_info.setText("Waiting");
      bt_download_button.setText("Pause");
  }

  @Override
  public void onPaused() {
      bt_download_button.setText("Continue");
      tv_download_info.setText("Paused");
  }

  @Override
  public void onDownloading(long progress, long size) {
      tv_download_info
              .setText(FileUtil.formatFileSize(progress) + "/" + FileUtil
                      .formatFileSize(size));
      bt_download_button.setText("Pause");
  }

  @Override
  public void onRemoved() {
      bt_download_button.setText("Download");
      tv_download_info.setText("");
      downloadInfo = null;
  }

  @Override
  public void onDownloadSuccess() {
      bt_download_button.setText("Delete");
      tv_download_info.setText("Download success");
  }

  @Override
  public void onDownloadFailed(DownloadException e) {
      bt_download_button.setText("Continue");
      tv_download_info.setText("Download fail:" + e.getMessage());
  }
});

//submit download info to download manager.
downloadManager.download(downloadInfo);