SharedPreferences web example

main.dart

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({
    super.key,
    required this.title,
  });

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  late final Counter counter;

  @override
  Widget build(context) => FutureBuilder<Counter>(
      future: SharedCounter.instance(),
      builder: (context, counter) {
        return switch (counter.connectionState) {
          ConnectionState.done => Scaffold(
              appBar: AppBar(
                backgroundColor: Theme.of(context).colorScheme.inversePrimary,
                title: Text(widget.title),
              ),
              body: Center(
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    ValueListenableBuilder<int>(
                      valueListenable: counter.data!,
                      builder: (context, count, _) => Text(
                        '$count',
                        style: Theme.of(context).textTheme.headlineMedium,
                      ),
                    ),
                  ],
                ),
              ),
              floatingActionButton: FloatingActionButton(
                onPressed: () => counter.data!.value++,
                tooltip: 'Increment',
                child: const Icon(Icons.add),
              ), // This trailing comma makes auto-formatting nicer for build methods.
            ),
          _ => const CircularProgressIndicator(),
        };
      });
}

abstract class Counter extends ValueListenable<int> with ChangeNotifier {
  @override
  int get value;
  set value(int value);
}

final class SharedCounter extends Counter {
  SharedCounter._(this._prefs, String key) : _key = key;
  final SharedPreferences _prefs;
  final String _key;

  static Future<SharedCounter> instance({String key = 'COUNTER'}) async =>
      SharedCounter._(await SharedPreferences.getInstance(), key);

  @override
  int get value => _prefs.getInt(_key) ?? 0;

  @override
  set value(int value) {
    _prefs.setInt(_key, value);
    notifyListeners();
  }
}

pubspec.yaml

name: issue_149023
description: ''
publish_to: 'none'
version: 1.0.0+1

environment:
  sdk: '>=3.4.1 <4.0.0'

dependencies:
  flutter:
    sdk: flutter
  shared_preferences: ^2.2.3

dev_dependencies:
  flutter_lints: ^3.0.0

flutter:
  uses-material-design: true