Progress bar inside custom dialog fragment - How to pass progress from an AsyncTask?

I have created a custom dialog fragment, inside it I have placed a progress bar. The host activity has an AsyncTask which uploads some images to a server. What I need is a way to pass the progress to the progress dialog fragment, I have tried via variables but it launches the fragmet again and again as the progress changes.

How could I pass the progress values without re launching the dialog fragment while values are changing?

I have tried with an interface as well, but it won't initialise my listener (the listener is always null).

my asyncTask (loopj):

private UploadProgressListener progressListener;

    public interface UploadProgressListener { 
        public void onProgress(int position, int length);       
    }

    //Interface to send selected image's position for deletion
    public void setUploadProgressListener(UploadProgressListener listener) {  
        this.progressListener = listener;  
    } 

....

    client.post("http://ift.tt/1G7kFqj", params,
                    new AsyncHttpResponseHandler() {

                        @Override
                        public void onFailure(int arg0, Header[] arg1, byte[] arg2,
                                Throwable arg3) {
                            System.out.println("Upload failed!" + arg3
                                    + " statys code: " + arg0);
                            if (arg0 == 0) {
                                System.out.println("Retrying Upload!");
                                sendZip();
                            }
                        }

                        @Override
                        public void onProgress(int position, int length) {

                            if(progressListener != null){
                            progressListener.onProgress(position, length);
                            }

                        }

                        @Override
                        public void onStart() {

                            // Show preloader dialog
                            DialogFragment newFragment = new PreloaderDialog();
                            newFragment.show(getSupportFragmentManager(),
                                    "preloader");
                        }

                        @Override
                        public void onSuccess(int arg0, Header[] arg1, byte[] arg2) {
                            System.out.println("Success!");
                            Toast.makeText(context, "Multumim pentru Comanda!",
                                    Toast.LENGTH_LONG).show();
                            finish();
                            datasource.deleteAllRows();
                        }
                    });

and the progress dialog fragment:

public class PreloaderDialog extends DialogFragment implements UploadProgressListener {

    private Builder v;
    private ProgressBar uploadProgress;
    int position;
    int length;

    /*
    public PreloaderDialog() {
        this.position = position;
        this.length = length;
    }
    */

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        LayoutInflater inflater = getActivity().getLayoutInflater();
        View view = inflater.inflate(R.layout.preloader_dialog, null);

        builder.setView(view);

        OrderActivity progressChanged = new OrderActivity();
        progressChanged.setUploadProgressListener(new UploadProgressListener() {

            @Override
            public void onProgress(int position, int length) {
                System.out.println("changed");

            }
        });

        uploadProgress = (ProgressBar) view.findViewById(R.id.uploadProressbar);

        // Create the AlertDialog object and return it
        return builder.create();
    }


    @Override
    public void onProgress(int position, int length) {
        //uploadProgress.setMax(length);
       // uploadProgress.setProgress(position);
        //System.out.println("progresspos: " + position);

    }