Flutter riverpod, StateNotifierProvider 初始化 StateNotifier 最佳实践

Question

I want to initialise a my StateNotifier asynchronously.

I think I can do it, I just want to check what I am doing is best practice.

This is a bit pseudo but hopefully makes sense...

final signInProvider = StateNotifierProvider<ExampleNotifier, SignInState>((ref) {
  return ExampleNotifier();
});

class ExampleNotifier extends StateNotifier<SignInState> {


  //emits loading state to start with

  ExampleNotifier() : super(Loading()) {
    //We then invoke a function that gets some data... from an api
    getAsyncDate();
  }


  void getAsyncDate() async {
    final foo = await someAsyncCall();

    //once its returned we set the state to it...
    state = foo;
  }

}

Basically is it ok to use the constructor invoke a function that will then set the state on the StateNotifier?

Thanks

Answer 1

Yes, it's great practice. The new version of Riverpod 2.0 has a class AsyncNotifier<State> (like as StateNotifier<State> ):

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

class SignInNotifier extends AsyncNotifier<void> {
  // Override the [build] method to return a [FutureOr]
  @override
  FutureOr<void> build() {
    // Return a value (or do nothing if the return type is void)
  }

  Future<void> signIn() async {
    // Read the repository using ref
    final authRepository = ref.read(authRepositoryProvider);
    // Set the loading state
    state = const AsyncLoading();
    // Sign in and update the state (data or error)
    state = await AsyncValue.guard(authRepository.signIn);
  }
}

The provider for this class looks like this:

// Using a constructor tear-off:
final signInProvider = AsyncNotifierProvider<SignInNotifier, void>(SignInNotifier.new)

Note how the function that creates the provider doesn't have a ref argument.

However, ref is always accessible as a property inside Notifier or AsyncNotifier subclasses, making it easy to read other providers.

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More info:

How-does-asyncnotifier-work

AsyncNotifier-class