如何使用下载管理器下载图像和音频，即使应用程序在后台关闭

import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Environment;
import android.os.IBinder;
import android.app.DownloadManager;
import android.app.DownloadManager.Request;

public class DownloadService extends Service {
    private DownloadManager downloadManager;

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        String imageUrl = intent.getStringExtra("image_url");
        String audioUrl = intent.getStringExtra("audio_url");

        downloadFile(imageUrl);
        downloadFile(audioUrl);

        return START_STICKY;
    }

    private void downloadFile(String url) {
        Uri uri = Uri.parse(url);

        DownloadManager.Request request = new DownloadManager.Request(uri);
        request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI | DownloadManager.Request.NETWORK_MOBILE);
        request.setAllowedOverRoaming(false);
        request.setTitle("Downloading file");
        request.setDescription("Downloading file...");
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
        request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, uri.getLastPathSegment());

        downloadManager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
        downloadManager.enqueue(request);
    }

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
}

Intent intent = new Intent(this, DownloadService.class);
intent.putExtra("image_url", "http://example.com/image.jpg");
intent.putExtra("audio_url", "http://example.com/audio.mp3");
startService(intent);