Flutter statelessWidget init a viewModel

Question

class RegisterPage extends StatelessWidget { 
final  String code; 

RegisterPage(this.code,);

RegisterViewModel _viewModel = RegisterViewModel();
}

//this is  RegisterViewModel

class RegisterViewModel extends ViewStateModel {
String code;
RegisterViewModel.fromCode(String code) {
 this.code = code;
}
}

but, there is a error.Sorry for the first question. enter image description here