try {
                    listener = new XMLRPCCallback() {
                        @Override
                        public void onResponse(long id, Object result) {
                            if(iConexion==id) {
                                code = String.valueOf(result);
                                Vibrator vibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
                                if (vibrator != null) {
                                    vibrator.vibrate(100);
                                }
                                Intent WindowCode = new Intent(MainActivity.this, WindowCode.class);
                                WindowCode.putExtra(Constantes.CODE, code);
                                startActivity(WindowCode);
                            }else{
                                Log.e("ID","Se han producido varios errores");
                            }
                        }

iConexion = client.callAsync(listener, Constantes.SERVER_PHP, new Object[]{user, passw});