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

​

class MyApp extends StatelessWidget {

  final _notifier = ValueNotifier<ThemeModel>(ThemeModel(ThemeMode.light));

​

  @override

  Widget build(BuildContext context) {

    return ValueListenableBuilder<ThemeModel>(

      valueListenable: _notifier,

      builder: (_, model, __) {

        final mode = model.mode;

        return MaterialApp(

          theme: ThemeData.light(), // Provide light theme.

          darkTheme: ThemeData.dark(), // Provide dark theme.

          themeMode: mode, // Decides which theme to show.

          home: Scaffold(

            appBar: AppBar(title: Text('Light/Dark Theme')),

            body: RaisedButton(

              onPressed: () => _notifier.value = ThemeModel(mode == ThemeMode.light ? ThemeMode.dark : ThemeMode.light),

              child: Text('Toggle Theme'),

            ),

          ),

        );

      },

    );

  }

}

​

class ThemeModel with ChangeNotifier {

  final ThemeMode _mode;

  ThemeMode get mode => _mode;

​

  ThemeModel(this._mode);

}

​

import 'package:flutter/material.dart';

​

void main() {

  runApp(

    MyApp(),

  );

}

​

class MyApp extends StatefulWidget {

  @override

  _MyAppState createState() => _MyAppState();

}

​

class _MyAppState extends State<MyApp> {

  bool _isDarkMode = false;

  String my_text = "Click the button below to toggle dark mode";

  Icon my_icon = Icon(Icons.light_mode);

​

  void _toggleDarkMode() {

    setState(() {

      _isDarkMode = !_isDarkMode;

      if (_isDarkMode == false) {

        my_text = "Click the button below to toggle dark mode";

        my_icon = Icon(Icons.light_mode);

      } else {

        my_text = "Click the button below to toggle light mode";

​

        my_icon = Icon(Icons.dark_mode);

      }

    });

  }

​

  @override

  Widget build(BuildContext context) {

    return MaterialApp(

      theme: _isDarkMode ? ThemeData.dark() : ThemeData.light(),

      home: Scaffold(

        appBar: AppBar(

          title: Text('Dark Mode Example'),

        ),

        body: Center(

          child: Column(

            mainAxisAlignment: MainAxisAlignment.center,

            children: [

              Icon(my_icon.icon),

              Text(my_text),

              ElevatedButton(

                onPressed: _toggleDarkMode,

                child: Text('Toggle Dark Mode'),

              ),

            ],

          ),

        ),

      ),

    );

  }

}

​