Why the automatic Riverpod provider for a StateNotifier is not a StateNotifierProvider?

Question

I'm writting a Flutter app with Riverpod architecture and I need a StateNotifier to keep track of an int that serve to save the current page of a multiscreen form.

Here is my StateNotifier code :

import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:riverpod_annotation/riverpod_annotation.dart';

part 'multi_step_controller.g.dart';

class MultiStepFormController extends StateNotifier<int> {
  MultiStepFormController() : super(0);

  void next() => state += 1;
  void previous() => state -= 1;
  void reset() => state = 0;
  void setIndex(int index) => state = index;
}

I wanted to use the Riverpod 3.0 syntax to automaticaly write the provider for this class with this code (and a build of course to generate the part file):

@Riverpod(keepAlive: true)
MultiStepFormController multiStepFormController(MultiStepFormControllerRef ref) {
  return MultiStepFormController();
}

But I end up with this error when I want to read the int : pageController.jumpToPage(currentIndex); The argument type 'MultiStepController' can't be assigned to the parameter type 'int'.

Instead, I changed the code for the provider by manually writting this : final multiStepFormControllerProvider = StateNotifierProvider<MultiStepFormController, int>((ref) { return MultiStepFormController(); });

And now the code works as intended.

I just want to know why the automatic provider doesn't work like the one I wrote by hand so I can have a better use of automatic generated code from Riverpod in the future. Thanks in advance ! ;-)

Sorry for the code preview, I can't format it properly...

Answer 1

The generator doesn't support StateNotifier. Use a Notifier/AysncNotifier instead.

Below is the syntax for defining an equivalent Notifier using code generation.

@riverpod
class MultiStepFormController extends _$MultiStepFormController {
  @override
  int build() => 0;

  void next() => state += 1;
  void previous() => state -= 1;
  void reset() => state = 0;
  void setIndex(int index) => state = index;
}

Use ref.watch(multiStepFormControllerProvider) to watch the Notifier's state.

Use ref.read(multiStepFormControllerProvider.notifier) to access the Notifier.

And remember not to declare a constructor for a Notifier/AysncNotifier class. The Notifier/AysncNotifier should be initialised using the build method.