前言
Adaptive Theme 这个组件通过包裹 MaterialApp 的方式整体管理 theme 主题，实现如下功能：
1.切换 light、dark、system 三种模式
2.自定义色彩
3.保存主题选择
4.开启调试按钮

步骤
安装配置
https://pub.dev/packages/adaptive_theme
pubspec.yaml

dependencies:
  flutter:
    sdk: flutter
    
  adaptive_theme: ^3.6.0

lib/main.dart

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

  @override
  Widget build(BuildContext context) {
    return AdaptiveTheme(
      light: ThemeData.light(useMaterial3: true),
      dark: ThemeData.dark(useMaterial3: true),
      initial: AdaptiveThemeMode.light,
      debugShowFloatingThemeButton: true,
      builder: (theme, darkTheme) => MaterialApp(
        title: 'Flutter Demo',
        theme: theme,
        darkTheme: darkTheme,
        home: const MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}

debugShowFloatingThemeButton 开启调试按钮

设置主题
设置亮色

ElevatedButton(
  onPressed: () {
    AdaptiveTheme.of(context).setLight();
  },
  child: const Text('Set Light Theme'),
),

设置暗色

ElevatedButton(
  onPressed: () {
    AdaptiveTheme.of(context).setDark();
  },
  child: const Text('Set Dark Theme'),
),

设置系统

ElevatedButton(
  onPressed: () {
    AdaptiveTheme.of(context).setSystem();
  },
  child: const Text('Set System Theme'),
),

toggle 切换

ElevatedButton(
  onPressed: () {
    AdaptiveTheme.of(context).toggleThemeMode();
  },
  child: const Text('Toggle Theme Mode'),
),

重置样式

ElevatedButton(
  onPressed: () {
    AdaptiveTheme.of(context).reset();
  },
  child: const Text('Reset Theme'),
),

监听样式切换

// 监听当前样式
ValueListenableBuilder(
  valueListenable: AdaptiveTheme.of(context).modeChangeNotifier,
  builder: (_, mode, child) {
    return Text(mode.modeName);
  },
),

自定义样式颜色

ElevatedButton(
  onPressed: () {
    AdaptiveTheme.of(context).setTheme(
      light: ThemeData(
        useMaterial3: true,
        brightness: Brightness.light,
        colorSchemeSeed: Colors.green,
      ),
      dark: ThemeData(
        useMaterial3: true,
        brightness: Brightness.dark,
        colorSchemeSeed: Colors.brown,
      ),
    );
  },
  child: const Text('Change Theme Color'),
),

读取配置

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final savedThemeMode = await AdaptiveTheme.getThemeMode();
  runApp(MyApp(savedThemeMode: savedThemeMode));
}
class MyApp extends StatelessWidget {
  final AdaptiveThemeMode? savedThemeMode;

  const MyApp({super.key, this.savedThemeMode});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return AdaptiveTheme(
      light: ThemeData.light(useMaterial3: true),
      dark: ThemeData.dark(useMaterial3: true),
      initial: savedThemeMode ?? AdaptiveThemeMode.light,
      debugShowFloatingThemeButton: true,
      builder: (theme, darkTheme) => MaterialApp(
        title: 'Flutter Demo',
        theme: theme,
        darkTheme: darkTheme,
        home: const MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}

不要覆盖 key
本地离线采用 shared_preferences 组件，所以不要覆盖键值 adaptive_theme_preferences

https://github.com/BirjuVachhani/adaptive_theme/blob/main/lib/src/adaptive_theme.dart

  /// Key used to store theme information into shared-preferences. If you want
  /// to persist theme mode changes even after shared-preferences
  /// is cleared (e.g. after log out), do not remove this [prefKey] key from
  /// shared-preferences.
  static const String prefKey = 'adaptive_theme_preferences';

代码
https://github.com/ducafecat/flutter_develop_tips/tree/main/flutter_application_adaptive_theme

小结
通过使用 Flutter 的 adaptive_theme 组件，我们可以轻松地实现应用主题的切换功能。该组件提供了简单的方法来手动设置浅色或深色主题，并且还可以根据系统定义的主题进行自适应切换。无论是在用户界面上还是在代码层面上，我们可以灵活地控制应用程序的主题外观，为用户提供更好的体验。

感谢阅读本文!