Pattern pattern =
                                      r'^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$';
                                  RegExp regex = new RegExp(pattern);
                                  if (!regex.hasMatch(value))
                                    return 'Please make sure your email address is valid';
                                  else
                                    return null;