Flutter Theme Switcher

main.dart

import 'package:flutter/material.dart';
/// Dart data model
class AppThemeValues {
  final Color primaryColor;
  final Color primaryBackgroundColor;

  AppThemeValues(
      {required this.primaryColor, required this.primaryBackgroundColor});
}

AppThemeValues ligthTheme = AppThemeValues(
  primaryColor: Color.fromARGB(255, 0, 0, 0),
  primaryBackgroundColor: Color.fromARGB(255, 255, 255, 255),
);

AppThemeValues darkTheme = AppThemeValues(
  primaryColor: Color.fromARGB(255, 255, 255, 255),
  primaryBackgroundColor: Color.fromARGB(255, 0, 0, 0),
);

class AppTheme extends InheritedWidget {
  final AppThemeValues value;
  AppTheme({required Widget child, required this.value}) : super(child: child);

  @override
  bool updateShouldNotify(covariant AppTheme oldWidget) {
    return true;
  }
}

/// Flutter Context Value Reading
class PrimaryHeading extends StatelessWidget {
  final String title;

  const PrimaryHeading({Key? key, required this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    var appTheme = context.dependOnInheritedWidgetOfExactType<AppTheme>()!;
    return Text(
      title,
      style: TextStyle(color: appTheme.value.primaryColor),
    );
  }
}

/// Main App
class AppThemeSwitcher extends StatefulWidget {
  const AppThemeSwitcher({Key? key}) : super(key: key);

  @override
  _AppThemeSwitcherState createState() => _AppThemeSwitcherState();
}

/// Main App State Widget
class _AppThemeSwitcherState extends State<AppThemeSwitcher> {
  AppThemeValues currentTheme = ligthTheme;

  @override
  Widget build(BuildContext context) {
    return AppTheme(
      value: currentTheme,
      child: Container(
        color: currentTheme.primaryBackgroundColor,
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            PrimaryHeading(
              title: "Theme Switcher",
            ),
            TextButton(
                onPressed: () {
                  setState(() {
                    currentTheme =
                        currentTheme == ligthTheme ? darkTheme : ligthTheme;
                  });
                },
                child: Container(
                  color: currentTheme.primaryColor,
                  child: Text(
                    "Change Theme",
                    style:
                        TextStyle(color: currentTheme.primaryBackgroundColor),
                  ),
                ))
          ],
        ),
      ),
    );
  }
}


/// Flutter boilerplate, not relevant for Context 
/// ==============================================
void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [Expanded(child:AppThemeSwitcher())]),
      ),
    );
  }
}

/// End Flutter boilerplate 
/// ==============================================