Themes plus persistence

main5.dart

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'package:shared_preferences/shared_preferences.dart'; //STEP 4 - Import shared_preferences

void main() {
  Get.lazyPut<ThemeController>(
      () => ThemeController()); //STEP 5 - lazy create ThemeController
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    ThemeController.to
        .getThemeModeFromPreferences(); //STEP 6 - Get saved theme at startup
    return GetMaterialApp(
      title: 'Theme change using Get',
      theme: ThemeData.light().copyWith(primaryColor: Colors.green),
      darkTheme: ThemeData.dark().copyWith(primaryColor: Colors.purple),
      themeMode: ThemeMode.system,
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

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

class _MyHomePageState extends State<MyHomePage> {
  ThemeMode _themeMode;

  @override
  Widget build(BuildContext context) {
    _themeMode = ThemeController
        .to.themeMode; //STEP 7 - get the theme from ThemeController
    print('${MediaQuery.of(context).platformBrightness}');
    print('${Theme.of(context).brightness}');
    return Scaffold(
      appBar: AppBar(),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.start,
        children: <Widget>[
          Center(
            child: Text(
              'System Brightness: ${Get.mediaQuery.platformBrightness.toString()}',
              style: TextStyle(fontSize: 20),
            ),
          ),
          SizedBox(height: 24),
          Center(
            child: Text(
              'Theme Brightness: ${Get.theme.brightness.toString()}',
              style: TextStyle(fontSize: 20),
            ),
          ),
          SizedBox(height: 24),
          Text(
            'ThemeMode',
            style: TextStyle(fontSize: 20),
            textAlign: TextAlign.left,
          ),
          RadioListTile(
            title: Text('system'),
            value: ThemeMode.system,
            groupValue: _themeMode,
            onChanged: (value) {
              setState(() {
                _themeMode = value;
                ThemeController.to
                    .setThemeMode(_themeMode); //STEP 8 - change this line
              });
            },
          ),
          RadioListTile(
            title: Text('dark'),
            value: ThemeMode.dark,
            groupValue: _themeMode,
            onChanged: (value) {
              setState(() {
                _themeMode = value;
                ThemeController.to.setThemeMode(_themeMode);
              });
            },
          ),
          RadioListTile(
            title: Text('light'),
            value: ThemeMode.light,
            groupValue: _themeMode,
            onChanged: (value) {
              setState(() {
                _themeMode = value;
                ThemeController.to.setThemeMode(_themeMode);
              });
            },
          ),
        ],
      ),
    );
  }
}

//STEP 9 - add our ThemeController
class ThemeController extends GetController {
  static ThemeController get to => Get.find();

  SharedPreferences prefs;
  ThemeMode _themeMode;
  ThemeMode get themeMode => _themeMode;

  Future<void> setThemeMode(ThemeMode themeMode) async {
    Get.changeThemeMode(themeMode);
    _themeMode = themeMode;
    update();
    prefs = await SharedPreferences.getInstance();
    await prefs.setString('theme', themeMode.toString().split('.')[1]);
  }

  getThemeModeFromPreferences() async {
    ThemeMode themeMode;
    prefs = await SharedPreferences.getInstance();
    String themeText = prefs.getString('theme') ?? 'system';
    try {
      themeMode =
          ThemeMode.values.firstWhere((e) => describeEnum(e) == themeText);
    } catch (e) {
      themeMode = ThemeMode.system;
    }
    setThemeMode(themeMode);
  }
}