MVPVMS pattern - by Simon Lightfoot :: #HumpdayQandA on 7th May 2025 :: https://www.youtube.com/watch?v=CqmhwUnesvQ

humpday_2025-05-04_2.dart

// MIT License
//
// Copyright (c) 2025 Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import 'package:flutter/material.dart';

void main() {
  runApp(App());
}

class App extends StatefulWidget {
  const App({super.key});

  static HomeRepository homeRepoOf(BuildContext context) {
    return context.findRootAncestorStateOfType<_AppState>()!.homeRepository;
  }

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  late HomeRepository homeRepository;

  @override
  void initState() {
    super.initState();
    homeRepository = HomeRepository();
  }

  ThemeData createTheme(Color seedColor) {
    final data = ThemeData.from(
      colorScheme: ColorScheme.fromSeed(seedColor: seedColor),
      useMaterial3: false,
    );
    return data.copyWith(
      bottomNavigationBarTheme: data.bottomNavigationBarTheme.copyWith(
        backgroundColor: seedColor,
        unselectedItemColor: Colors.white,
        selectedItemColor: Colors.blue.shade200,
        type: BottomNavigationBarType.shifting,
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: createTheme(Colors.deepPurple.shade600),
      home: Home(),
    );
  }
}

class HomeRepository {
  const HomeRepository();

  Future<List<String>> loadHomeData() async {
    // Example loading delay
    await Future.delayed(const Duration(seconds: 3));
    return [
      for (int index = 0; index < 1000; index++) //
        'Home Item #$index',
    ];
  }
}

class HomePresenter extends ChangeNotifier {
  HomePresenter();

  var _viewModel = HomeViewModel.initial;

  HomeViewModel get viewModel => _viewModel;

  void load(HomeRepository homeRepo) async {
    final data = await homeRepo.loadHomeData();
    _viewModel = _viewModel.copyWith(
      title: 'Home',
      isLoading: false,
      items: data,
    );
    notifyListeners();
  }

  void adminLogin() {
    _viewModel = _viewModel.copyWith(isAdmin: true);
    notifyListeners();
  }

  void updateSortOrder(HomeSortOrder order) {
    final compare = switch (order) {
      HomeSortOrder.ascending => (String a, String b) => a.compareTo(b),
      HomeSortOrder.descending => (String a, String b) => b.compareTo(a),
    };
    _viewModel = _viewModel.copyWith(
      items: List.of(_viewModel.items)..sort(compare),
    );
    notifyListeners();
  }

  void updateNavigation(int index) {
    _viewModel = _viewModel.copyWith(navIndex: index);
    notifyListeners();
  }
}

abstract class ViewModel {
  const ViewModel();
}

class HomeViewModel extends ViewModel {
  const HomeViewModel({
    required this.title,
    required this.isAdmin,
    required this.navIndex,
    required this.isLoading,
    required this.items,
  });

  static const initial = HomeViewModel(
    title: 'Loading',
    isAdmin: false,
    navIndex: 0,
    isLoading: true,
    items: [],
  );

  final String title;
  final bool isAdmin;
  final int navIndex;
  final bool isLoading;
  final List<String> items;

  HomeViewModel copyWith({
    String? title,
    bool? isAdmin,
    int? navIndex,
    bool? isLoading,
    List<String>? items,
  }) {
    return HomeViewModel(
      title: title ?? this.title,
      isAdmin: isAdmin ?? this.isAdmin,
      navIndex: navIndex ?? this.navIndex,
      isLoading: isLoading ?? this.isLoading,
      items: items ?? this.items,
    );
  }
}

class Home extends StatefulWidget {
  const Home({super.key});

  @override
  State<Home> createState() => _HomeState();
}

class _HomeState extends State<Home> {
  final presenter = HomePresenter();

  @override
  void initState() {
    super.initState();
    presenter.load(App.homeRepoOf(context));
  }

  @override
  void dispose() {
    presenter.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return ListenableBuilder(
      listenable: presenter,
      builder: (BuildContext context, Widget? child) {
        return Scaffold(
          appBar: AppBar(
            title: Text(presenter.viewModel.title),
            actions: [
              HomeOverflowMenu(
                onLoginPressed: presenter.adminLogin,
                onChanged: presenter.updateSortOrder,
              ),
            ],
          ),
          body: presenter.viewModel.isLoading
              ? Center(
                  child: CircularProgressIndicator.adaptive(),
                )
              : ListView.builder(
                  itemCount: presenter.viewModel.items.length,
                  itemBuilder: (BuildContext context, int index) {
                    final item = presenter.viewModel.items[index];
                    return ListTile(title: Text(item));
                  },
                ),
          bottomNavigationBar: BottomNavigationBar(
            type: BottomNavigationBarType.fixed,
            currentIndex: presenter.viewModel.navIndex,
            onTap: presenter.updateNavigation,
            items: [
              BottomNavigationBarItem(
                icon: Icon(Icons.home),
                label: 'Home',
              ),
              BottomNavigationBarItem(
                icon: Icon(Icons.feed),
                label: 'Feed',
              ),
              BottomNavigationBarItem(
                icon: Icon(Icons.person),
                label: 'Profile',
              ),
              if (presenter.viewModel.isAdmin) //
                BottomNavigationBarItem(
                  icon: Icon(Icons.lock_person),
                  label: 'Admin',
                ),
            ],
          ),
        );
      },
    );
  }
}

enum HomeSortOrder {
  ascending,
  descending,
}

class HomeOverflowMenu extends StatelessWidget {
  const HomeOverflowMenu({
    super.key,
    required this.onLoginPressed,
    required this.onChanged,
  });

  final VoidCallback onLoginPressed;
  final ValueChanged<HomeSortOrder> onChanged;

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        IconButton(
          onPressed: onLoginPressed,
          icon: Icon(Icons.login),
        ),
        MenuAnchor(
          menuChildren: [
            MenuItemButton(
              onPressed: () => onChanged(HomeSortOrder.ascending),
              leadingIcon: Icon(Icons.sort_by_alpha),
              child: Text('Ascending'),
            ),
            MenuItemButton(
              onPressed: () => onChanged(HomeSortOrder.descending),
              leadingIcon: Icon(Icons.sort_by_alpha),
              child: Text('Descending'),
            ),
          ],
          builder: (BuildContext context, MenuController controller, Widget? child) {
            return IconButton(
              onPressed: () => controller.open(),
              icon: Icon(Icons.sort),
            );
          },
        ),
      ],
    );
  }
}