如何在Android中同时下载多个文件

Question

我有一个活动,它有两个listview.第一个listview有音乐.第二个列表视图显示下载项目,每个下载项目显示下载百分比的进度条.如果用户单击音乐项,我将下载项添加到第二个列表视图并使用AsyncTask启动下载文件.用户可以点击多个音乐,这意味着同时下载多个文件.我可以使用AsyncTask下载文件.但我想下载服务中的文件因为下载必须继续甚至应用程序关闭.

我不知道如何与服务同时下载多个文件.我应该遵循哪些步骤？有没有这方面的教程？

Answer 1

我在我的一个制作应用程序中实现了相同的功能:

1. 创建一个表以添加要下载的项目.排序应基于添加项目以供下载的时间.将此视为队列.还要添加一列以检查文件是否已下载.如果已下载,则将其从队列中删除.
2. 创建一个IntentService即使应用程序关闭也将负责在后台下载数据.这Service应该一直运行,直到表队列不为空.它应该仅在添加新项目时启动,或者当网络连接状态从无效更改为实时时启动.在此范围内,Service您应该检查队列是否为空.如果为空,则从表中提取N个行以添加到queue(ExecutorService)中进行下载.检查网络状态的chnage创建一个BroadcastReceiverwith ?LocalBroadcastManager.

3. 现在您可以在DownloadIntentService中编写代码.尝试根据您的需要进行修改:

   private static int NUMBER_OF_CORES =
       Runtime.getRuntime().availableProcessors() * 2;
   private final ExecutorService executorService;
   private final ExecutorCompletionService<DownloadModel> executorCompletionService;
   
   public DownloadIntentService() {
   super("DownloadIntentService");
   executorService = Executors.newFixedThreadPool(NUMBER_OF_CORES);
   executorCompletionService = new ExecutorCompletionService<>(executorService);
   }
   
   ......
   @Override
   protected void onHandleIntent(Intent intent) {  
   
   //Check to see for storage permission
   if (ActivityCompat.checkSelfPermission(this,
           Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED
           && ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
           == PackageManager.PERMISSION_GRANTED) {
    .....
    //Now create job queue
    ....
   //Fetch rows to download from table
   DownloadQuery downloadQuery = new DownloadQuery(DownloadIntentService.this);
   
   ArrayList<DownloadModel> downloadModelArrayList = downloadQuery.getDownload(DownloadContract.IFileDownloadStatus.NOT_DOWNLOADED,
               0, NUMBER_OF_CORES);
   //Check if queue contains any item
   if (downloadModelArrayList.size() > 0) {
   if (!executorService.isShutdown())
                       executorCompletionService.submit(new DownloadWorkerCallable(**Your download model from table to download**, DownloadIntentService.this));
   }
   .....
   //Don't forget to shutdown the executorService
   }
   }
   

这DownloadWorkerCallable是实现Runnable实际下载文件.