Riverpod StateProvider select vs watch

readme.md

Riverpod StateProvider select vs watch

Created with <3 with dartpad.dev.

main.dart

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

void main() {
  runApp(
    const ProviderScope(child: MyApp()),
  );
}

final sourceProvider = StateProvider((ref) => 0);

final watchProvider = FutureProvider<int>((ref) async {
  // I would expect that this provider would only update when the value of sourceProvider
  // changes.
  // Instead it updates whenever the sourceProvider updates, even when the value is equal to the previous
  // value
  final source = ref.watch(sourceProvider);
  await Future.delayed(const Duration(seconds: 2));
  return source;
}, dependencies: [
  sourceProvider,
]);

final selectProvider = FutureProvider<int>((ref) async {
  // this provider uses select to prevent unncessary rebuilds when the updated value is the same
  final source = ref.watch(sourceProvider.select((v) => v));
  await Future.delayed(const Duration(seconds: 2));
  return source;
}, dependencies: [
  sourceProvider,
]);

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyHomePage(),
    );
  }
}

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

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Riverpod example'),
      ),
      body: Row(
        children: [
          Expanded(
            child: ContentWidget(data: ref.watch(watchProvider)),
          ),
          Expanded(
            child: ContentWidget(data: ref.watch(selectProvider)),
          ),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => ref.refresh(sourceProvider),
        tooltip: 'Refresh',
        child: const Icon(Icons.refresh),
      ),
    );
  }
}

class ContentWidget extends ConsumerWidget {
  final AsyncValue<int> data;
  const ContentWidget({Key? key, required this.data}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return Center(
      child: data.map(
        data: (it) => Text(it.value.toString()),
        loading: (it) => const Text("Loading"),
        error: (error) => const Text("error"),
      ),
    );
  }
}