在AsyncTask上显示对话框（Looper.prepare（））

Question

HY！我有一个asynctask下载3文件frm互联网。 在下载中，我正在显示进度条。 现在我把这个asynctask放到另一个，它会产生一个错误。 无法在没有调用Looper.prepare（）

的线程中创建处理程序

但是如果我在“预先执行”下载工作时调用Looper.prepare（），但我没有看到对话框。 想法为什么？

这是异步方法的代码

private class DownloadFilesTask extends AsyncTask<String, Integer, String> {



        protected void onPreExecute() {
        super.onPreExecute();

        System.out.println("Mostro la dialog");
        Looper.prepare();
        showDialog(1);

        Toast.makeText(getApplicationContext(), "Download file in corso. il player verrà aperto al termine", Toast.LENGTH_LONG).show();
        System.out.println("Mostrata");
        pDialog.setOnCancelListener(new DialogInterface.OnCancelListener(){
            public void onCancel(DialogInterface dialog) {
                //DownloadFilesTask().cancel(true);
                System.out.println("Ho chiuso la finestra durante il download dei file");
             myTask.cancel(true);
            }
      });
        pDialog.setProgress(0);
    }

    protected String doInBackground(String... string) {

        int count;
        int lenghtOfFile = 0;
        try {

            URL url;
            URLConnection conection;
            long total = 0;

            if(fi3!=0){
             url = new URL(string[2]);
                 conection = url.openConnection();
                 conection.connect();
                 lenghtOfFile += conection.getContentLength();
            }
            if(fi2!=0){
                 url = new URL(string[1]);
                 conection = url.openConnection();
                 conection.connect();
                 lenghtOfFile += conection.getContentLength();
            }
            if(fi1!=0){
             url = new URL(string[0]);
                 conection = url.openConnection();
                 conection.connect();

             //download primo file

            InputStream input = new BufferedInputStream(url.openStream(), 8192);

            File cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"mp3 Scaricati");
            if(!cacheDir.exists())
               cacheDir.mkdirs();

            File f=new File(cacheDir,file1);
            // Output stream to write file
            OutputStream output = new FileOutputStream(f);

            byte data[] = new byte[1024];



            while ((count = input.read(data)) != -1) {
                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();

            if(isCancelled()) return null;

             }else{
                 System.out.println("Il file " + file1 + " è già presente");
             }

            //download secondo file

             if (fi2!=0) {
                 System.out.println("Il file non esiste: " +file2);
            url = new URL(string[1]);
            conection = url.openConnection();
           conection.connect();

           InputStream input = new BufferedInputStream(url.openStream(), 8192);

           File cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"mp3 Scaricati");
            if(!cacheDir.exists())
               cacheDir.mkdirs();

            File f=new File(cacheDir,file2);

            OutputStream  output = new FileOutputStream(f);

            byte data1[] = new byte[1024];


           while ((count = input.read(data1)) != -1) {
               total += count;

               publishProgress((int)((total*100)/lenghtOfFile));


               output.write(data1, 0, count);
           }

           output.flush();

           // closing streams
           output.close();
           input.close();

           if(isCancelled()) return null;

             }else{
                 System.out.println(file2 + "già presente");
             }

           //Dowload terzo file
             if (fi3!=0) {
                 System.out.println("Il file non esiste: " +file3);
           url = new URL(string[2]);
           conection = url.openConnection();
           conection.connect();
          // getting file length
          // lenghtOfFile = conection.getContentLength();

           //Fine calcolo dimensione file


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

           File cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"mp3 Scaricati");
             if(!cacheDir.exists())
               cacheDir.mkdirs();

            File f=new File(cacheDir,file3);
          // Output stream to write file
            OutputStream   output = new FileOutputStream(f);

           byte datan[] = new byte[1024];
          while ((count = input.read(datan)) != -1) {
              total += count;
              // publishing the progress....
              // After this onProgressUpdate will be called
              publishProgress((int)((total*100)/lenghtOfFile));

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

          // flushing output
          output.flush();

          // closing streams
          output.close();
          input.close();
             } else{
                 System.out.println(file3 + "già presente");
             }

          if(isCancelled()) return null;

        } catch (Exception e) {
            Log.e("Error: ", e.getMessage());
        }

            return null;
    }

    protected void onProgressUpdate(Integer... progress) {

         if (isCancelled()){ return;}
         else{ pDialog.setProgress(progress[0]);

         }
    }

    protected void onPostExecute(String result) {
        pDialog.dismiss();
        //Avvio il player
        Toast.makeText(getApplicationContext(), "Download completo, avvio il player", Toast.LENGTH_LONG).show();

       startActivity(StartPlayer);

    }
    }


protected Dialog onCreateDialog(int id) {
   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();
    return pDialog;

}