Flutter ThemeProvider with persistent storage

theme_provider.dart

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

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  final prefs = await SharedPreferences.getInstance();

  runApp(App(
    themeController: ThemeController(prefs),
  ));
}

class App extends StatelessWidget {
  const App({
    super.key,
    required ThemeController themeController,
  }) : _themeController = themeController;

  final ThemeController _themeController;

  @override
  Widget build(BuildContext context) {
    return ThemeProvider(
      controller: _themeController,
      builder: (context, _) => MaterialApp(
        darkTheme: ThemeData(brightness: Brightness.dark),
        themeMode: _themeController.currentTheme,
        title: "ThemeProvider",
        home: const Scaffold(body: Center(child: ChoiceTheme())),
      ),
    );
  }
}

class ThemeController extends ChangeNotifier {
  static const themePrefKey = 'theme';

  ThemeController(this._prefs) {
    _currentTheme = switch (_prefs.getString(themePrefKey)) {
      'system' => ThemeMode.system,
      'light' => ThemeMode.light,
      'dark' => ThemeMode.dark,
      _ => ThemeMode.system,
    };
  }

  final SharedPreferences _prefs;
  late ThemeMode _currentTheme;

  ThemeMode get currentTheme => _currentTheme;

  void setTheme(ThemeMode theme) {
    _currentTheme = theme;
    _prefs.setString(themePrefKey, theme.name);
    notifyListeners();
  }

  static ThemeController of(BuildContext context) {
    final provider = context.getInheritedWidgetOfExactType<ThemeProvider>();
    return (provider as ThemeProvider).controller;
  }
}

class ThemeProvider extends InheritedWidget {
  ThemeProvider({
    super.key,
    required this.controller,
    required Widget Function(BuildContext, Widget?) builder,
  }) : super(child: AnimatedBuilder(animation: controller, builder: builder));

  final ThemeController controller;

  @override
  bool updateShouldNotify(ThemeProvider oldWidget) =>
      controller != oldWidget.controller;
}

class ChoiceTheme extends StatefulWidget {
  const ChoiceTheme({super.key});

  @override
  State<ChoiceTheme> createState() => _ChoiceThemeState();
}

class _ChoiceThemeState extends State<ChoiceTheme> {
  @override
  Widget build(BuildContext context) {
    return SegmentedButton(
      segments: <ButtonSegment<ThemeMode>>[
        ButtonSegment(
            value: ThemeMode.light, label: Text(ThemeMode.light.name)),
        ButtonSegment(
            value: ThemeMode.system, label: Text(ThemeMode.system.name)),
        ButtonSegment(value: ThemeMode.dark, label: Text(ThemeMode.dark.name)),
      ],
      selected: {ThemeController.of(context).currentTheme},
      onSelectionChanged: (Set<ThemeMode> newSelection) => setState(() {
        ThemeController.of(context).setTheme(newSelection.first);
      }),
    );
  }
}