Why do we need ChangeNotifierProvider instead of just using a ChangeNotifier?

Question

I am trying to learn how to use flutter_riverpod for state management, I am having trouble understanding what the "need" for ChangeNotifierProvider is , same thing for StateNotifierProvider. Let's take the following ChangeNotifier for example :

class CounterNotifier extends ChangeNotifier {
  int value = 0;

  void increment() {
    value++;
    notifyListeners();
  }
}

Why is it "advised" to declare a ChangeNotifierProvider for my ChangeNotifier and use it to watch() and read() the value of my ChangeNotifier like so:

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

final counterProvider = ChangeNotifierProvider((ref) => CounterNotifier());


class ChangeCounterPage extends ConsumerWidget {
  const ChangeCounterPage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: () {
        
          ref.read(counterProvider).increment();
        },
        child: const Icon(Icons.add),
      ),
      body: Center(
       
        child: Text(ref.watch(counterProvider).value.toString()),
      ),
    );
  }
}

Why not just use the ChangeNotifier (like we do with provider) ? in the official documentation of riverpod it says : " we are using the ChangeNotifierProvider to allow the UI to interact with our ChangeNotifier class." -> what does that mean ? is ChangeNotifierProvider a widget that wraps around the ChangeNotifier and thus makes is "visible" in the widget tree ? I've also read that it makes the "manipulation" of our state easier or more manageable but I can't understand why or how it is needed.

score 2 · Accepted Answer · answered Jun 09 '23 at 04:16

A ChangeNotifier must be listened, with an action associated with change events, in order to be useful. It also must be unlistened before the listener goes away.

A ChangeNotifierProvider wraps the process of listening to a ChangeNotifier into a "ProviderListener" protocol, which knows how to make the widget watching the provider rebuild when events occur, and how to disconnect itself when the widget is disposed.

Why do we need ChangeNotifierProvider instead of just using a ChangeNotifier?

1 Answers1