add dark mode

cupertino_gallery/lib/gallery_home.dart

@@ -3,7 +3,14 @@ import 'settings_page.dart';
 import 'widgets_page.dart';
 
 class GalleryHome extends StatelessWidget {
-  const GalleryHome({super.key});
+  const GalleryHome({
+    super.key,
+    required this.onThemeChange,
+    required this.isDarkMode,
+  });
+
+  final ValueChanged<bool> onThemeChange;
+  final bool isDarkMode;
 
   @override
   Widget build(BuildContext context) {
@@ -25,7 +32,10 @@ class GalleryHome extends StatelessWidget {
           builder: (BuildContext context) {
             return switch (index) {
               0 => const WidgetsPage(),
-              1 => const SettingsPage(),
+              1 => SettingsPage(
+                    onThemeChange: onThemeChange,
+                    isDarkMode: isDarkMode,
+                  ),
               _ => const Center(child: Text('Widgets')),
             };
           },

cupertino_gallery/lib/main.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
 
 import 'gallery_home.dart';
 
@@ -10,11 +11,33 @@ void main() {
   runApp(const CupertinoGalleryApp());
 }
 
-class CupertinoGalleryApp extends StatelessWidget {
+class CupertinoGalleryApp extends StatefulWidget {
   const CupertinoGalleryApp({super.key});
 
+  @override
+  State<CupertinoGalleryApp> createState() => _CupertinoGalleryAppState();
+}
+
+class _CupertinoGalleryAppState extends State<CupertinoGalleryApp> {
+  ThemeMode _themeMode = ThemeMode.system;
+
+  void _handleThemeChange(bool isDarkMode) {
+    setState(() {
+      _themeMode = isDarkMode ? ThemeMode.dark : ThemeMode.light;
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
-    return const CupertinoApp(title: 'Cupertino Gallery', home: GalleryHome());
+    return CupertinoApp(
+      title: 'Cupertino Gallery',
+      theme: CupertinoThemeData(
+        brightness: _themeMode == ThemeMode.dark ? Brightness.dark : Brightness.light,
+      ),
+      home: GalleryHome(
+        onThemeChange: _handleThemeChange,
+        isDarkMode: _themeMode == ThemeMode.dark,
+      ),
+    );
   }
 }

cupertino_gallery/lib/settings_page.dart

@@ -1,22 +1,39 @@
 import 'package:flutter/cupertino.dart';
 
 class SettingsPage extends StatefulWidget {
-  const SettingsPage({super.key});
+  const SettingsPage({
+    super.key,
+    required this.onThemeChange,
+    required this.isDarkMode,
+  });
+
+  final ValueChanged<bool> onThemeChange;
+  final bool isDarkMode;
 
   @override
   State<SettingsPage> createState() => _SettingsPageState();
 }
 
 class _SettingsPageState extends State<SettingsPage> {
-  bool _darkMode = false;
   double _textSize = 1.0;
+  late bool isDarkMode;
+
+  @override
+  void initState() {
+    isDarkMode = widget.isDarkMode;
+    super.initState();
+  }
+
+  @override
+  void didChangeDependencies() {
+    isDarkMode = widget.isDarkMode;
+    super.didChangeDependencies();
+  }
 
   @override
   Widget build(BuildContext context) {
     return CupertinoPageScaffold(
-      navigationBar: const CupertinoNavigationBar(
-        middle: Text('Settings'),
-      ),
+      navigationBar: const CupertinoNavigationBar(middle: Text('Settings')),
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.start,
         children: [
@@ -26,10 +43,11 @@ class _SettingsPageState extends State<SettingsPage> {
               CupertinoListTile(
                 title: const Text('Dark Mode'),
                 trailing: CupertinoSwitch(
-                  value: _darkMode,
-                  onChanged: (bool value) {
+                  value: isDarkMode,
+                  onChanged: (bool isActive) {
                     setState(() {
-                      _darkMode = value;
+                      isDarkMode = isActive;
+                      widget.onThemeChange(isActive);
                     });
                   },
                 ),
@@ -75,7 +93,8 @@ class _SettingsPageState extends State<SettingsPage> {
                     builder: (BuildContext context) => CupertinoAlertDialog(
                       title: const Text('Reset Settings'),
                       content: const Text(
-                          'Are you sure you want to reset all settings?'),
+                        'Are you sure you want to reset all settings?',
+                      ),
                       actions: <CupertinoDialogAction>[
                         CupertinoDialogAction(
                           child: const Text('Cancel'),
@@ -88,7 +107,7 @@ class _SettingsPageState extends State<SettingsPage> {
                           child: const Text('Reset'),
                           onPressed: () {
                             setState(() {
-                              _darkMode = false;
+                              widget.onThemeChange(false);
                               _textSize = 1.0;
                             });
                             Navigator.pop(context);