Build a flutter theme switcher with riverpod

#flutter #riverpod #theme #dart

With this article, I added dark and light themes in the MaterialApp.

Material 3 theme recipe for the flutter app

Jhin Lee ・ Oct 30 '22

#flutter #m3 #theme #material

Now it's time to add a toggle switch in the app. I'll use riverpod. One of the famous framework people uses for state management. As expressed in the official document, It's more caching framework itself, but It's helpful to cache the global states.

Setup the riverpod

Add the riverpod package
```
flutter pub add flutter_riverpod
```

Wrap the MainApp with the ProviderScope
From:

void main() {
  runApp(const MyApp());
}

To:

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

Implement the theme toggle switch

Add the themeModeProvider

final themeModeProvider = StateProvider<ThemeMode>((ref) {
  return ThemeMode.dark;
});

Convert the MyApp as ConsumerWidget and watch the provider

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

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final themMode = ref.watch(themeModeProvider);
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        useMaterial3: true,
        colorScheme: lightColorScheme,
        textTheme: textTheme,
      ),
      darkTheme: ThemeData(
        useMaterial3: true,
        colorScheme: darkColorScheme,
        textTheme: textTheme,
      ),
      themeMode: themMode, // Apply them theme
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

Every time the themeModeProvider changes, the widget rebuilds and assigns the new value to the themeMode

final themMode = ref.watch(themeModeProvider);

Add the toggle button

Consumer(builder: (context, ref, child) {
  final theme = ref.watch(themeModeProvider);
  return IconButton(
      onPressed: () {
        ref.read(themeModeProvider.notifier).state =
            theme == ThemeMode.light
                ? ThemeMode.dark
                : ThemeMode.light;
      },
      icon: Icon(theme == ThemeMode.dark
          ? Icons.light_mode
          : Icons.dark_mode));
})