即使按下後退按鈕，也不會停止在AsynchTask上

Question

我正在下載AsynchTask中的pdf文件，因此它下載文件時，我的進度對話框正在更新。然而，問題是，如果我按下後退按鈕比我的警報箱彈出，下載停止在後臺。我希望即使在調用警報對話框後它仍應繼續下載，或者一旦警報彈出後暫停下載，並在單擊警報對話框的取消按鈕時繼續下載一次。

這裏是一個片段，

@Override 
protected Dialog onCreateDialog(int id) 
{ 
switch (id) 
{ 
    case progress_bar_type: 
    pDialog = new ProgressDialog(this); 
    pDialog.setMessage("Downloading file. Please wait..."); 
    pDialog.setIndeterminate(false); 
    pDialog.setMax(100); 
    pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); 
    pDialog.setCancelable(true); 
    pDialog.show(); 
    pDialog.setOnKeyListener(new DialogInterface.OnKeyListener() 
    { 
    @Override 
    public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) 
    { 
    if(keyCode == KeyEvent.KEYCODE_BACK) 
    { 
    running = false; 

     AlertDialog.Builder alertDialog = new AlertDialog.Builder(context); 
     AlertDialog.setIcon(R.drawable.ic_launcher); 
     alertDialog.setTitle("Ariisto"); 
     alertDialog.setMessage("Do you Want to Cancel the Download ?"); 
    alertDialog.setCancelable(true); 
    alertDialog.setPositiveButton("YES", new DialogInterface.OnClickListener() 
     { 
     @Override 
public void onClick(DialogInterface dialog, int which) 
{ 
           // TODO Auto-generated method stub 

           File externalFile = new File(Environment.getExternalStorageDirectory(),"downloadedfile.pdf"); 
           externalFile.delete(); 
           pDialog.dismiss(); 
           running = false; 
           Log.d("External File", "DELETED"); 
           pDialog.setProgress(0); 
           count = 2; 


          } 
         }); 
         alertDialog.setNegativeButton("NO", new DialogInterface.OnClickListener() { 

          @Override 
          public void onClick(DialogInterface dialog, int which) { 
           // TODO Auto-generated method stub 
           new DownloadFileFromURL().execute(file_url); 
           running = true; 
           count = 0; 
          } 
         }); 

         AlertDialog alert = alertDialog.create(); 

          alert.show(); 

        } 

        return false; 

       } 
      }); 


      return pDialog; 
     default: 
      return null; 
     } 
    } 
    class DownloadFileFromURL extends AsyncTask<String, String, String> 
    { 

     /** 
     * Before starting background thread 
     * Show Progress Bar Dialog 
     * */ 




     @SuppressWarnings("deprecation") 
     protected void onPreExecute() 
     { 
      super.onPreExecute(); 
      showDialog(progress_bar_type); 
      publishProgress(""+(int)(0)); 
      running = true; 
     } 

     @Override 
     protected void onCancelled() { 
      // TODO Auto-generated method stub 

      Log.d("------------","iNSIDE ON CANCELLED METHOD"); 

      super.onCancelled(); 
     } 



     @Override 
     protected String doInBackground(String... file_url) 
     { 
      // TODO Auto-generated method stub 
      int count; 
      try 
      { 
       URL url = new URL(file_url[0]); 
       URLConnection connection = url.openConnection(); 
       connection.connect(); 
       // getting file length 
       int lenghtOfFile = connection.getContentLength(); 

       // input stream to read file - with 8k buffer 
       InputStream input = new BufferedInputStream(url.openStream(), 8192); 

       // Output stream to write file 
       FileOutputStream output = new FileOutputStream("/sdcard/downloadedfile.pdf"); 


       byte data[] = new byte[1024]; 

       long total = 0; 

       while ( ((count = input.read(data)) != -1) && (running == true) ) 
       { 




        total += count; 

        // publishing the progress.... 
        // After this onProgressUpdate will be called 
        publishProgress(""+(int)((total*100)/lenghtOfFile)); 

        // writing data to file 
        output.write(data, 0, count); 
       } 

       output.flush(); 

       // closing streams 
       output.close(); 
       input.close(); 
      } 
      catch (Exception e) 
      { 
       Log.e("Error: ", " "+e.getMessage()); 
      } 
      return null; 
     } 

     protected void onProgressUpdate(String... progress) 
     { 
      // setting progress percentage 
      pDialog.setProgress(Integer.parseInt(progress[0])); 
     } 
     @SuppressWarnings("deprecation") 
     protected void onPostExecute(String file_url) 
     { 
      // dismiss the dialog after the file was downloaded 
      if(running == true){ 
       dismissDialog(progress_bar_type); 
       // Displaying downloaded image into image view 
       // Reading image path from sdcard 
       String imagePath = Environment.getExternalStorageDirectory().toString() + "/downloadedfile.pdf"; 
       // setting downloaded into image view 
       Log.d(imagePath, "show file"); 
       File file = new File(Environment.getExternalStorageDirectory(),"downloadedfile.pdf"); 
       Uri external = Uri.fromFile(file); 

       viewPdf(external); 
      } 
     } 

    } 

Answer 1

我有非常相似，這樣的要求。用戶將點擊一個listItem，一個AsyncTask將開始下載它，然後在完成時顯示它。如果用戶在下載完成之前點擊後退按鈕，則會顯示一個警告對話框，詢問是否中止下載。如果在顯示該對話框時下載完成，它將簡單地關閉對話框並完成該活動。我沒有時間去拉和消毒的代碼，但是模式如下：

的活動有兩個私有字段：

private DownloadTask downloader = null; 
private AlertDialog dlgCancel = null; 

在onBackPressed

：

if(downloader != null) { 
    dlgCancel =.... 
    dlgCancel.show(); 
} else 
    finish(); 

在

下載任務的onPostExecute：

if(isCancelled()) { 
    ... dismiss the download 
} else { 
    if(dlgCancel == null) { 
     ... handle the download here ... 
    } else { 
     dlgCancel.dismiss(); 
     dlgCancel = null; 
     Activity.finish(); 
    } 
} 

最後，在onClick for Abort-Download bu tton：

downloader.cancel(true); 
Activity.finish(); 

請注意，你需要留意isCancelled（）在你的AsyncTask的doInBackground（），這樣就可以儘可能快地作出反應。有些操作不會立即返回。