flutter_design_patterns/lib/main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(),
    );
  }
}

abstract class ListStrategy<T> {
  List<T> compose(List<T> items);
}

class Monkey {
  Monkey({required this.name, required this.power});
  final String name;
  final int power;

  @override
  String toString() => '$name - Power: $power';
}

class GreatestMonkeyStrategy implements ListStrategy<Monkey> {
  @override
  List<Monkey> compose(List<Monkey> items) {
    return [
      items.fold<Monkey>(
          Monkey(name: '', power: 0), (aMonkey, bMonkey) => aMonkey.power > bMonkey.power ? aMonkey : bMonkey)
    ];
  }
}

class WeakMonkeysStrategy implements ListStrategy<Monkey> {
  @override
  List<Monkey> compose(List<Monkey> items) {
    return items
        .where(
          (element) => element.power <= 200,
        )
        .toList();
  }
}

List<Monkey> monkeys = [
  Monkey(name: 'Mortimer', power: 25),
  Monkey(name: 'ApeMan', power: 354),
  Monkey(name: 'Spider', power: 65),
  Monkey(name: 'DK', power: 500),
  Monkey(name: 'Tim', power: 120),
  Monkey(name: 'Kong', power: 25400),
];

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

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ListStrategy listStrat = WeakMonkeysStrategy();

  void swapStrategies() {
    if (listStrat.runtimeType == WeakMonkeysStrategy) {
      setState(() => listStrat = GreatestMonkeyStrategy());
      return;
    }
    setState(() => listStrat = WeakMonkeysStrategy());
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: const Text('Abstract Factory'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text('All monkeys:'),
            ...monkeys
                .map(
                  (e) => Text(e.toString()),
                )
                .toList(),
            const SizedBox(height: 50),
            Text(listStrat.runtimeType.toString()),
            ...listStrat
                .compose(monkeys)
                .map(
                  (e) => Text(e.toString()),
                )
                .toList(),
            const SizedBox(height: 100),
            ElevatedButton(onPressed: () => swapStrategies(), child: const Text('Change Strats')),
          ],
        ),
      ),
    );
  }
}