samples/material_3_demo/lib/main.dart

// Copyright 2021 The Flutter team. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

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

import 'constants.dart';
import 'home.dart';

void main() {
  runApp(
    const App(),
  );
}

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

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  bool useMaterial3 = true;
  ThemeMode themeMode = ThemeMode.system;
  ColorSeed colorSelected = ColorSeed.baseColor;

  bool get useLightMode {
    switch (themeMode) {
      case ThemeMode.system:
        return SchedulerBinding.instance.window.platformBrightness ==
            Brightness.light;
      case ThemeMode.light:
        return true;
      case ThemeMode.dark:
        return false;
    }
  }

  void handleBrightnessChange(bool useLightMode) {
    setState(() {
      themeMode = useLightMode ? ThemeMode.light : ThemeMode.dark;
    });
  }

  void handleMaterialVersionChange() {
    setState(() {
      useMaterial3 = !useMaterial3;
    });
  }

  void handleColorSelect(int value) {
    setState(() {
      colorSelected = ColorSeed.values[value];
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Material 3',
      themeMode: themeMode,
      theme: ThemeData(
        colorSchemeSeed: colorSelected.color,
        useMaterial3: useMaterial3,
        brightness: Brightness.light,
      ),
      darkTheme: ThemeData(
        colorSchemeSeed: colorSelected.color,
        useMaterial3: useMaterial3,
        brightness: Brightness.dark,
      ),
      home: Home(
        useLightMode: useLightMode,
        useMaterial3: useMaterial3,
        colorSelected: colorSelected,
        handleBrightnessChange: handleBrightnessChange,
        handleMaterialVersionChange: handleMaterialVersionChange,
        handleColorSelect: handleColorSelect,
      ),
    );
  }
}