Cubit for app state management example

cubit.dart

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

void main() {
  runApp(
    BlocProvider(
      create: (context) => ShoppingCartCubit(),
      child: const MyApp(),
    ),
  );
}

const List<Item> inventory = [
  Item(name: "Shirt", cost: 12.99),
  Item(name: "Shoes", cost: 120.00),
  Item(name: "Pants", cost: 63.74),
  Item(name: "Hat", cost: 8.23),
];

typedef Cart = List<Item>;

class CartState {
  final List<Item> itemsInCart;

  CartState(this.itemsInCart);
}

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

  @override
  Widget build(BuildContext context) {
    return ListView(
      shrinkWrap: true,
      physics: const ClampingScrollPhysics(),
      children: [
        Text(
          'Inventory',
          style: Theme.of(context).textTheme.displayMedium,
        ),
        ListView.builder(
          shrinkWrap: true,
          physics: const ClampingScrollPhysics(),
          itemCount: inventory.length,
          itemBuilder: (BuildContext context, int i) => Card(
            child: ListTile(
              title: Text(inventory[i].name),
              subtitle: Text('\$${inventory[i].cost.toStringAsFixed(2)}'),
              trailing: IconButton(
                icon: const Icon(Icons.add_shopping_cart),
                onPressed: () => context.read<ShoppingCartCubit>().add(
                      inventory[i],
                    ),
              ),
            ),
          ),
        ),
      ],
    );
  }
}

class Item {
  final double cost;
  final String name;

  const Item({
    required this.cost,
    required this.name,
  });
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Padding(
          padding: const EdgeInsets.all(8.0),
          child: ListView(
            children: const [
              Inventory(),
              ShoppingCart(),
            ],
          ),
        ),
      ),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return BlocBuilder<ShoppingCartCubit, CartState>(
      builder: (BuildContext context, CartState cart) {
        final List<Item> uniqueItemsInCart =
            context.read<ShoppingCartCubit>().uniqueItemsInCart;
        final double totalCost = context.read<ShoppingCartCubit>().totalCost;
        return ListView(
          shrinkWrap: true,
          physics: const ClampingScrollPhysics(),
          children: [
            Text(
              'Shopping Cart',
              style: Theme.of(context).textTheme.displayMedium,
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                Text('Items in Cart: ${cart.itemsInCart.length}'),
                Text('Total Cost: \$${totalCost.toStringAsFixed(2)}'),
                OutlinedButton.icon(
                  label: const Text('Clear cart'),
                  icon: const Icon(Icons.remove_shopping_cart),
                  onPressed: () =>
                      context.read<ShoppingCartCubit>().clearCart(),
                ),
              ],
            ),
            ListView.builder(
              shrinkWrap: true,
              physics: const ClampingScrollPhysics(),
              itemCount: uniqueItemsInCart.length,
              itemBuilder: (context, i) {
                return Card(
                  child: ListTile(
                    leading: Text(
                        '${cart.itemsInCart.where((element) => element == uniqueItemsInCart[i]).length} ×'),
                    title: Text(uniqueItemsInCart[i].name),
                    subtitle: Text(
                        '\$${uniqueItemsInCart[i].cost.toStringAsFixed(2)}'),
                  ),
                );
              },
            ),
          ],
        );
      },
    );
  }
}

class ShoppingCartCubit extends Cubit<CartState> {
  ShoppingCartCubit() : super(CartState([]));

  double get totalCost {
    double price = 0;
    for (Item item in state.itemsInCart) {
      price += item.cost;
    }

    return price;
  }

  List<Item> get uniqueItemsInCart {
    final List<Item> unique = [];
    for (Item item in state.itemsInCart) {
      if (!unique.contains(item)) {
        unique.add(item);
      }
    }
    return unique;
  }

  void add(Item item) {
    final after = state.itemsInCart..add(item);

    emit(CartState(after));
  }

  void clearCart() {
    emit(CartState([]));
  }
}