Android : Download a file using asynctask and showing progressbar

i have a following code to download an image , show a progress bar and return its bitmap. but the bitmap always returns null.. once i remove the while loop, the bitmap has value, but i dont get a progress bar.

@Override
protected Bitmap doInBackground(String... params) {
    bitmap = null;

    try {
        URL url = new URL(params[0]);
        HttpURLConnection connection = (HttpURLConnection) url
                .openConnection();
        connection.setDoInput(true);
        connection.connect();
        int lenghtOfFile = connection.getContentLength();
        InputStream input = connection.getInputStream();
        OutputStream output = new FileOutputStream(Environment
                .getExternalStorageDirectory().toString()
                + "/DCIM/downloadedfile.jpg");

        byte data[] = new byte[1024];

        long total = 0;

        int count;
        while ((count = input.read(data)) != -1) {
            total += count;
            publishProgress((int) ((total * 100) / lenghtOfFile));
            output.write(data, 0, count);

        }

        Bitmap bitmap = BitmapFactory.decodeStream(input);

        return bitmap;

    } catch (IOException e) {

        Log.e("could not  load ", e.getMessage());
        e.printStackTrace();
        return null;
    }

}

protected void onProgressUpdate(Integer... progress) {
    pDialog.setProgress(progress[0]);
}

public void onPostExecute(Bitmap result) {
    pDialog.dismiss();
    listener.onTaskCompleted(result);
}
enter code here