Theme Manager example using InheritedWidget

home.dart

import 'package:flutter/material.dart';
import 'package:example/state.dart';

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        elevation: 10,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            ElevatedButton(
              onPressed: () {
                final manager = AppSettingsManager.of(context);
                manager?.setTheme(ThemeMode.dark);
              },
              child: const Text('Tema Oscuro'),
            ),
            const SizedBox(height: 20),
            ElevatedButton(
              onPressed: () {
                final manager = AppSettingsManager.of(context);
                manager?.setTheme(ThemeMode.light);
              },
              child: const Text('Tema Claro'),
            ),
            const SizedBox(height: 20),
            ElevatedButton(
              onPressed: () {
                final manager = AppSettingsManager.of(context);
                manager?.setTheme(ThemeMode.system);
              },
              child: const Text('Tema del Sistema'),
            ),
          ],
        ),
      ),
    );
  }
}

main.dart

import 'package:flutter/material.dart';
import 'package:example/home.dart';
import 'package:example/state.dart';

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

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

  @override
  Widget build(BuildContext context) {
    AppSettings? settingsManager = AppSettingsManager.of(context);

    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      darkTheme: ThemeData(
        colorScheme: ColorScheme.fromSeed(
          seedColor: Colors.deepPurple,
          brightness: Brightness.dark,
        ),
        useMaterial3: true,
      ),
      themeMode: settingsManager?.themeMode,
      home: const MyHomePage(title: 'State'),
      // home: const HomeScreen(),
      debugShowCheckedModeBanner: false,
    );
  }
}

state.dart

import 'package:flutter/material.dart';

class AppSettingsManager extends StatefulWidget {
  const AppSettingsManager({
    super.key,
    required this.child,
  });

  final Widget child;

  static AppSettings? of(BuildContext context) {
    AppSettings? appSettingsState =
        context.dependOnInheritedWidgetOfExactType<AppSettings>();
    return appSettingsState;
  }

  @override
  State<AppSettingsManager> createState() => AppSettingsManagerState();
}

class AppSettingsManagerState extends State<AppSettingsManager> {
  ThemeMode mode = ThemeMode.system;

  setTheme(ThemeMode newMode) {
    mode = newMode;
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return AppSettings(
      themeMode: mode,
      setTheme: setTheme,
      child: widget.child,
    );
  }
}

// Inherited que notifica estado
class AppSettings extends InheritedWidget {
  const AppSettings({
    super.key,
    required super.child,
    required this.themeMode,
    required this.setTheme,
  });

  final ThemeMode themeMode;
  final Function(ThemeMode) setTheme;

  @override
  bool updateShouldNotify(AppSettings oldWidget) {
    return themeMode != oldWidget.themeMode;
  }
}

Este ejemplo permite almacenar en un estado a nivel de app la configuración con el modo del tema (ThemeMode.light, ThemeMode.dark o ThemeMode.system) y modificarlo desde otras partes del árbol de la aplicación para que los cambios se propaguen a donde sea necesario.

Ejemplo de la aplicación en funcionamiento: