avoid_notifier_constructors

v0.4.0 Warning Bloc / Riverpod

This rule flags Notifier and AsyncNotifier subclasses that have constructors with non-empty bodies or initializer lists. Empty constructors are allowed. All initialization logic should go into the build() method instead.

Why use this rule

Riverpod creates and recreates Notifiers as part of its lifecycle management. The build() method is the proper place for initialization because it runs at the right time in the provider lifecycle and has access to ref. Constructor logic runs before the Notifier is fully wired up, which means you can’t use ref there, and the logic won’t re-run when the provider is refreshed or invalidated.

See also: Riverpod Notifier documentation

Don’t

import 'package:riverpod/riverpod.dart';

// Constructor with body
class BadCounter extends Notifier<int> {
  var _initial = 0;

  BadCounter() {
    _initial = 1;
  }

  @override
  int build() => _initial;
}

// Constructor with initializer list
class BadCounter2 extends Notifier<int> {
  final int _initial;

  BadCounter2() : _initial = 1;

  @override
  int build() => _initial;
}

Do

import 'package:riverpod/riverpod.dart';

// No constructor, initialization in build()
class GoodCounter extends Notifier<int> {
  @override
  int build() => 0;

  void increment() => state++;
}

// Empty constructor is fine
class GoodCounter2 extends Notifier<int> {
  GoodCounter2();

  @override
  int build() => 0;
}

Configuration

To disable this rule:

plugins:
  many_lints:
    diagnostics:
      avoid_notifier_constructors: false