使用AsyncTask下载多个文件？

Question

我想使用AsyncTask下载多个文件。 我通过通知栏中的进度条开始每次下载一个AsyncTask，但是我面临很多问题。

1. 如果我下载4个或5个文件在一个或多个文件 中断，没有任何理由的同时。

2. 如果我下载4张或5张图片，一张或多张图片损坏。

这是我使用的代码。

private class DownloadFile extends AsyncTask<String, Integer, Long> 
      { 
       int nID = 0; 
       int nDownloadCounter = 0; 
       public DownloadFile(String sFileName, int nNotificationID) { 
        this.nID = nNotificationID; 
        this.NotificationName = sFileName; 
        this.nDownloadCounter = 0; 
       } 

       protected void onPreExecute(){ 
        this.sDownloadPath = sFilePathWithSubDir; 
        notification = new Notification(R.drawable.app_icon, "Download File", System.currentTimeMillis()); 
        RemoteViews contentView = new RemoteViews(getPackageName(), R.layout.custom_notification); 

        Intent notificationIntent = new Intent(); 
        File file = new File(this.sDownloadPath + this.NotificationName); 
        sMediaDataType = GSUtilities.sGetFileMIMEType(this.NotificationName); 

        notificationIntent.setAction(android.content.Intent.ACTION_VIEW); 
        notificationIntent.setDataAndType(Uri.fromFile(file), sMediaDataType); 

        PendingIntent contentIntent = PendingIntent.getActivity(getApplicationContext(), 0, notificationIntent, 0); 

        contentView.setTextViewText(R.id.status_percent, "0%"); 
        contentView.setTextViewText(R.id.status_fileName, this.NotificationName); 
        contentView.setProgressBar(R.id.status_progress, 100, 0, false); 

        notification.contentView = contentView; 
        notification.contentIntent = contentIntent; 
        mNotificationManager.notify(nID, notification);    
       } 

       protected Long doInBackground(String... urls) {  
        long retData = 0; 

        OutputStream fosXSPDatabse = null; 
        InputStream inServerResponse = null; 
        URLConnection oURLConnection = null; 
        URL oURL = null; 

        try 
        { 
         oURL = new URL(oFileManager.sExpiryLink); 
         oURLConnection = oURL.openConnection(); 

         if (!(oURLConnection instanceof HttpURLConnection)) 
          throw new IOException("Not an HTTP connection"); 

         oURLConnection.connect();    
         inServerResponse = new BufferedInputStream(oURL.openStream()); 
         if (inServerResponse != null) 
         { 
          File fDirectory = new File(oFileManager.sAppFlesDirectory); 
          if (!fDirectory.exists()) 
          { 
           if (!fDirectory.mkdir()) 
           {} 
          } 

          fosXSPDatabse = new FileOutputStream(oFileManager.sAppFlesDirectory + "/" + oFileInfo.getFileName()); 
          byte data[] = new byte[BUFFER_SIZE]; 

          int nCount = 0; 
          long lTotalDownloaded = 0; 
          int nTotalSize = oURLConnection.getContentLength(); 
          while ((nCount = inServerResponse.read(data)) != -1) 
          { 
           Log.d(String.valueOf(nID) + " - DoInBackground", String.valueOf(dNotificationbarProgress)); 
           nDownloadCounter ++; 
           lTotalDownloaded += nCount; 
           dNotificationbarProgress = lTotalDownloaded * 100.0/nTotalSize; 
           if (this.nDownloadCounter == 20 || dNotificationbarProgress == 100) { 
            publishProgress(Integer.parseInt(new DecimalFormat("#.##").format(dNotificationbarProgress).split("\\.")[0])); 
            nDownloadCounter = 0; 
           } 
           fosXSPDatabse.write(data, 0, nCount); 
          } 
          inServerResponse.close(); 
          fosXSPDatabse.flush(); 
          fosXSPDatabse.close(); 
         } 
        } 
        catch (MalformedURLException e) 
        {} 
        catch (IOException e) 
        {} 
        catch (Exception e) 
        {} 
        finally 
        { 
         try 
         { 
          inServerResponse.close(); 
          fosXSPDatabse.flush(); 
          fosXSPDatabse.close(); 

         } 
         catch (IOException e) 
         {} 
        } 

        return retData; 
       } 

       protected void onProgressUpdate(Integer... progress) { 
        try 
        { 
         Log.d(String.valueOf(nID),"onProgressUpdate"); 
         notification.contentView.setProgressBar(R.id.status_progress, 100, progress[0], false); 
         notification.contentView.setTextViewText(R.id.status_fileName, this.NotificationName); 
         notification.contentView.setTextViewText(R.id.status_percent, String.valueOf(progress[0]) + "%"); 

         Intent notificationIntent = new Intent(); 
         File file = new File(this.sDownloadPath + this.NotificationName); 
         sMediaDataType = GSUtilities.sGetFileMIMEType(this.NotificationName); 

         notificationIntent.setAction(android.content.Intent.ACTION_VIEW); 
         notificationIntent.setDataAndType(Uri.fromFile(file), sMediaDataType); 

         PendingIntent contentIntent = PendingIntent.getActivity(getApplicationContext(), 0, notificationIntent, 0); 
         notification.contentIntent = contentIntent; 
         mNotificationManager.notify(this.nID, notification);  
        } 
        catch(Exception e) 
        {} 
       } 

       protected void onPostExecute(Long result) { 
        notification.contentView.setTextViewText(R.id.status_fileName, "Successfully installed " + this.NotificationName); 
        notification.contentView.setTextViewText(R.id.status_percent, "100%"); 
        mNotificationManager.notify(this.nID, notification); 
       } 
      } 

Answer 1

处理下载多个文件的最佳方法是使用服务。

Answer 2

首先，这是不是一个好主意悄悄忽略例外。你应该至少将它们记录到logcat。它认为这是问题。

其次，您正在多次关闭流。

你从哪里调用AsyncTask？

如果它来自活动并且用户离开它，那么操作系统想要释放内存时可能会终止该操作。

如果它来自服务，也可能会终止，但至少会在稍后重新启动。如果服务是从一个不同的进程（如同步适配器）启动的，则还应将PreExecute和PublishProgress和PostExecute代码以应用程序循环处理程序作为消息发布到UI线程。

另外，尝试将并发下载数限制为最大3。否则，可能会发生OutOfMemory。你可以用BlockingQueue来做到这一点。如果并发不重要，请考虑使用IntentService而不是AsyncTask。