Three buttons, change icon (with GetIt and manager class)

get_it.dart

import 'package:final_exam/home_screen/home_screen_manager.dart';
import 'package:get_it/get_it.dart';

final getIt = GetIt.instance;

void setupGetIt() {
  getIt.registerLazySingleton(() => HomeScreenManager());
}

home_screen.dart

import 'package:final_exam/get_it.dart';
import 'package:flutter/material.dart';

import 'home_screen_manager.dart';

class HomeScreen extends StatefulWidget {
  const HomeScreen({Key? key}) : super(key: key);

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  final manager = getIt<HomeScreenManager>();

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          ValueListenableBuilder<MyIcon>(
              valueListenable: manager.iconNotifier,
              builder: (context, myIcon, child) {
                if (myIcon == MyIcon.sun) {
                  return Icon(Icons.sunny, size: 50);
                } else if (myIcon == MyIcon.cloud) {
                  return Icon(Icons.cloud, size: 50);
                } else {
                  return Icon(Icons.house, size: 50);
                }
              }),
          SizedBox(height: 20),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              ElevatedButton(
                onPressed: () {
                  manager.chooseHouse();
                },
                child: Text('House'),
              ),
              SizedBox(width: 20),
              ElevatedButton(
                onPressed: () {
                  manager.chooseSun();
                },
                child: Text('Sun'),
              ),
              SizedBox(width: 20),
              ElevatedButton(
                onPressed: () {
                  manager.chooseCloud();
                },
                child: Text('Cloud'),
              ),
            ],
          ),
        ],
      ),
    );
  }
}

home_screen_manager.dart

import 'package:flutter/material.dart';

class HomeScreenManager {
  final iconNotifier = ValueNotifier<MyIcon>(MyIcon.house);

  void chooseHouse() {
    iconNotifier.value = MyIcon.house;
  }

  void chooseSun() {
    iconNotifier.value = MyIcon.sun;
  }

  void chooseCloud() {
    iconNotifier.value = MyIcon.cloud;
  }
}

enum MyIcon {
  house,
  sun,
  cloud,
}

main.dart

import 'package:final_exam/get_it.dart';
import 'package:final_exam/home_screen/home_screen.dart';
import 'package:flutter/material.dart';

void main() {
  setupGetIt();
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: HomeScreen(),
    );
  }
}

pubspec.yaml

name: final_exam
description: A new Flutter project.
publish_to: 'none' 
version: 1.0.0+1

environment:
  sdk: ">=2.16.1 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  get_it: ^7.2.0

dev_dependencies:
  flutter_test:
    sdk: flutter
  flutter_lints: ^1.0.0

flutter:
  uses-material-design: true