What is the best way to use ChangeNotifier provider objects with the build method?

Question

I have a flutter application and I keep getting the error which states:

The following assertion was thrown while dispatching notifications for UserData:
setState() or markNeedsBuild() called during build.

UserData is a class that extends ChangeNotifier and this exception is thrown when I call the notifyListeners() method.

My View

class MyViewextends StatefulWidget {
  @override
  _MyViewState createState() => _MyViewState();
}

class _MyViewState extends State<MyView> {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
        future: UserService().getUser(),
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.done)
            {
              var userData = Provider.of<UserData>(context, listen: false);
              var user = (snapshot.data as ApiResponseModel)?.entity;
              userData.set(user); //this is where the error gets thrown
            }

          return Container(); 
          //shortened for question purposes. Ideally, I will be printing the User objects to the container. 
          //It containers String properties like firstName, lastName.
        });
  }
}

UserData

class UserData extends ChangeNotifier{
  UserDto user;

  void set(UserDto userDto){
    user = userDto;
    notifyListeners();
  }

What I want to know is, what better way can I initialise my UserDto object so this error is not thrown?

In my head, that if block made the most sense but apparently not.