flutter - Flutter statelessWidget 初始化 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;
}
}

但是，有一个错误。对不起第一个问题。在此处输入图像描述