ProgressDialog in AsyncTask zeigt keinen Fortschritt

Question

Obwohl ich viele Referenzen online überprüft habe, kann ich das Problem immer noch nicht finden. Es scheint die ProgressDialog scheint in Ordnung, aber immer wenn ich den Fortschritt aktualisieren möchten, in onProgressUpdate seine Instanz ist immer Null.

Das ist mein AsyncTask:

package com.async_tasks; 

public class UploadTask extends AsyncTask<Void,Integer,Void> implements Serializable {   
    private static final String TAG = UploadTask.class.getSimpleName(); 
    private ConnectionToServer _connectionToServer; 
    private TransferDetails _td; 
    private Activity _activity; 
    private ProgressDialog _progDialog; 
    private UploadTask _taskInstance; 

    public UploadTask(Activity activity, ConnectionToServer connectionToServer, TransferDetails td) { 

     _activity = activity; 
     _connectionToServer = connectionToServer; 
     _td = td; 
     _taskInstance = this; 
    } 

    @Override 
    protected void onPreExecute() { 

     _progDialog = new ProgressDialog(_activity); 
     String cancel = _context.getResources().getString(R.string.cancel); 

     _progDialog.setCancelable(false); 
     _progDialog.setTitle(_context.getResources().getString(R.string.uploading)); 
     _progDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER); 
     _progDialog.setProgress(0); 
     _progDialog.setMax(100); 
     _progDialog.setButton(DialogInterface.BUTTON_NEGATIVE, cancel, new DialogInterface.OnClickListener() { 
      @Override 
      public void onClick(DialogInterface dialog, int which) { 

       _taskInstance.cancel(true); 
      } 
     }); 

     _progDialog.show(); 

    } 

    @Override 
    protected Void doInBackground(Void... voids) { 

     //uploading file ... 
       float percent = (float) (fileSize - bytesToRead)/fileSize * 100; 
       publishProgress((int)percent);     
      } 

     } 
     catch (IOException e) { 
       // Handling exception 
     } finally { 

      if(bis!=null) { 
       try { 
        bis.close(); 
       } catch (IOException e) { 
        e.printStackTrace(); 
       } 
      } 
      clearMembers(); 

      } 
     } 

     return null; 
    } 

    @Override 
    protected void onProgressUpdate(Integer... progress) { 

     if(_progDialog!=null) { // <<------------ I suspect for some reason this is always false, as _progDialog is always null - But why?! 
      _progDialog.incrementProgressBy(progress[0]); 
     } 
    } 

    @Override 
    protected void onPostExecute(Void result) { 

     //The task is complete, clear members 
     clearMembers(); 
    } 

    private void clearMembers() { 

     _activity = null; 
     if(_progDialog!=null) { 
      _progDialog.dismiss(); 
      _progDialog = null; 
     } 
    } 
} 

Und das ist der Anruf von MainActivity:

TransferDetails td = (TransferDetails) report.data(); 
ConnectionToServer conn = StorageServerProxyService.getConn(); 
UploadTask uploadTask = new UploadTask(MainActivity.this, conn, td); 
uploadTask.execute(); 

Answer 1

die OnPreExecute ändern() -Methode wie folgt:

@Override 
    protected void onPreExecute() { 

progDialog = new ProgressDialog(ActivityName.this); 
     String cancel = _context.getResources().getString(R.string.cancel); 

     _progDialog.setCancelable(false); 
     _progDialog.setTitle(_context.getResources().getString(R.string.uploading)); 
     _progDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER); 
     _progDialog.setProgress(0); 
     _progDialog.setMax(100); 
     _progDialog.setButton(DialogInterface.BUTTON_NEGATIVE, cancel, new DialogInterface.OnClickListener() { 
      @Override 
      public void onClick(DialogInterface dialog, int which) { 

       _taskInstance.cancel(true); 
      } 
     }); 

     _progDialog.show(); 

    }