scaffolding

lib/theme/theme_service.dart

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+import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'themes.dart';
+
+class ThemeService {
+  ThemeService._();
+  static late SharedPreferences prefs;
+  static ThemeService? _instance;
+
+  static Future<ThemeService> get instance async {
+    if (_instance == null) {
+      prefs = await SharedPreferences.getInstance();
+      _instance = ThemeService._();
+    }
+    return _instance!;
+  }
+
+  final allThemes = <String, ThemeData>{
+    'dark': darkTheme,
+    'light': lightTheme,
+    'pink': pinkTheme,
+    'darkBlue': darkBlueTheme,
+    'halloween': halloweenTheme,
+  };
+
+  String get previousThemeName {
+    String? themeName = prefs.getString('previousThemeName');
+    if (themeName == null) {
+      final isPlatformDark =
+          WidgetsBinding.instance.window.platformBrightness == Brightness.dark;
+      themeName = isPlatformDark ? 'light' : 'dark';
+    }
+    return themeName;
+  }
+
+  get initial {
+    String? themeName = prefs.getString('theme');
+    if (themeName == null) {
+      final isPlatformDark =
+          WidgetsBinding.instance.window.platformBrightness == Brightness.dark;
+      themeName = isPlatformDark ? 'dark' : 'light';
+    }
+    return allThemes[themeName];
+  }
+
+  save(String newThemeName) {
+    var currentThemeName = prefs.getString('theme');
+    if (currentThemeName != null) {
+      prefs.setString('previousThemeName', currentThemeName);
+    }
+    prefs.setString('theme', newThemeName);
+  }
+
+  ThemeData getByName(String name) {
+    return allThemes[name]!;
+  }
+}

lib/theme/themes.dart

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+import 'package:flutter/material.dart';
+
+ThemeData lightTheme = ThemeData.light();
+
+ThemeData darkTheme = ThemeData.dark();
+
+ThemeData pinkTheme = lightTheme.copyWith(
+    primaryColor: const Color(0xFFF49FB6),
+    scaffoldBackgroundColor: const Color(0xFFFAF8F0),
+    floatingActionButtonTheme: const FloatingActionButtonThemeData(
+      foregroundColor: Color(0xFF24737c),
+      backgroundColor: Color(0xFFA6E0DE),
+    ),
+    textTheme: const TextTheme(
+      bodyText1: TextStyle(
+        color: Colors.black87,
+      ),
+    ));
+
+ThemeData halloweenTheme = lightTheme.copyWith(
+  primaryColor: const Color(0xFF55705A),
+  scaffoldBackgroundColor: const Color(0xFFE48873),
+  floatingActionButtonTheme: const FloatingActionButtonThemeData(
+    foregroundColor: Color(0xFFea8e71),
+    backgroundColor: Color(0xFF2b2119),
+  ),
+);
+
+ThemeData darkBlueTheme = ThemeData.dark().copyWith(
+  primaryColor: const Color(0xFF1E1E2C),
+  scaffoldBackgroundColor: const Color(0xFF2D2D44),
+  textTheme: const TextTheme(
+    bodyText1: TextStyle(
+      color: Color(0xFF33E1Ed),
+    ),
+  ),
+);