Flutter /Dart Classes

Question

I have implemented a class in a file user_service.dart:

class UserService { 
    Future<User> createUser(...)

 ....
}

I have tried referencing the createUser method in another class

I import the User Service class

  import 'user_service.dart';

and try

  UserService userService;
  print(userService.toString());

  UserService.createUser(....);

It compiles fine.

A am getting an error: NoSuchMethodError: The method 'createUser' was called on null.

Any ideas?

Help appreciated.

To access `createUser` you need an instance from `UserService` `UserService()` creates an instance. `UserService().createUser()` would work. If you don't want multiple `UserService` instances, you need to create it on a single place and pass it around or use something like a singleton pattern. https://stackoverflow.com/questions/12649573/how-do-you-build-a-singleton-in-dart — Günter Zöchbauer, Dec 19 '18 at 11:38
If you need to access createUser() method from the class UserService you can declare your method as a static member like this` static Future createUser(...) ;` — Saed Nabil, Dec 19 '18 at 11:58
Have you create an instance of that class? ```UserService service = UserService(); service.createUser()``` — Linh, Dec 19 '18 at 12:16
Did not create the instance - thank you. Using a singleton is also a good idea. — Kevin Dev, Dec 19 '18 at 13:29

Marcos Boaventura · Answer 1 · 2018-12-20T14:22:36.223

2

In your case you need firstly create a new instance of you UserService class.

UserService _instance = UserService(); // here you are creating a new instance with a default constructor

//now you can call your UserService methods
_instance.createUser();

edited Dec 20 '18 at 14:22

answered Dec 20 '18 at 11:13

Marcos Boaventura

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Flutter /Dart Classes

1 Answers1