Loja: Remover Itens

Parte da seção Projetos do Journey de Flutter da Coddy. Lição 26 de 36.

As pessoas mudam de ideia. Cada linha do carrinho ganha um botão de remoção que tira uma unidade daquele produto, e a linha desaparece quando não restar nenhuma.

void remove(Product product) {
  if (quantityOf(product) > 1) {
    _quantities[product] = quantityOf(product) - 1;
  } else {
    _quantities.remove(product);
  }
  notifyListeners();
}

Remover a chave do mapa quando a quantidade chega a 1, em vez de defini-la como 0, é o que faz a linha desaparecer: items são as chaves do mapa.

Agora, uma linha termina com duas coisas: o total e o botão. trailing recebe um widget, então coloque ambos em uma Row com mainAxisSize: MainAxisSize.min, que mantém a linha apenas tão larga quanto o conteúdo.

Um carrinho vazio merece um estado vazio, como a lista de tarefas tinha: um ícone suave de carrinho e uma linha de texto no lugar da lista.

Desafio

Médio

Permita que as pessoas removam itens:

adicione o método remove a CartModel
faça com que o trailing de cada linha seja uma Row com o total e um IconButton com Icons.remove_circle_outline que remova uma unidade
quando o carrinho estiver vazio, exiba um Icons.shopping_cart_outlined centralizado (tamanho 64, com a cor outline do tema), 12 pixels de espaço e Your cart is empty

Experimente você mesmo

import 'package:flutter/material.dart';
import 'package:intl/intl.dart';
import 'package:provider/provider.dart';

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

final money = NumberFormat.currency(locale: 'en_US', symbol: '\$');

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.orange),
      ),
      home: const ShopScreen(),
    );
  }
}

class Product {
  const Product({
    required this.name,
    required this.price,
    required this.icon,
    required this.color,
    required this.description,
  });

  final String name;
  final double price;
  final IconData icon;
  final MaterialColor color;
  final String description;
}

const List<Product> products = [
  Product(
    name: 'Headphones',
    price: 59,
    icon: Icons.headphones,
    color: Colors.indigo,
    description: 'Wireless headphones with 30 hours of battery.',
  ),
  Product(
    name: 'Watch',
    price: 129,
    icon: Icons.watch,
    color: Colors.teal,
    description: 'A smart watch that counts your steps.',
  ),
  Product(
    name: 'Backpack',
    price: 45.5,
    icon: Icons.backpack,
    color: Colors.orange,
    description: 'Room for a laptop, a lunch and a jacket.',
  ),
  Product(
    name: 'Mug',
    price: 12,
    icon: Icons.coffee,
    color: Colors.brown,
    description: 'Holds a big coffee and keeps it warm.',
  ),
  Product(
    name: 'Camera',
    price: 1299,
    icon: Icons.photo_camera,
    color: Colors.blueGrey,
    description: 'A mirrorless camera for sharp photos.',
  ),
  Product(
    name: 'Sneakers',
    price: 89.99,
    icon: Icons.directions_run,
    color: Colors.red,
    description: 'Light running shoes for every day.',
  ),
];

class CartModel extends ChangeNotifier {
  final Map<Product, int> _quantities = {};

  List<Product> get items => _quantities.keys.toList();
  int quantityOf(Product product) => _quantities[product] ?? 0;
  int get count => _quantities.values.fold(0, (sum, quantity) => sum + quantity);
  double get total => items.fold(0, (sum, product) => sum + product.price * quantityOf(product));

  void add(Product product) {
    _quantities[product] = quantityOf(product) + 1;
    notifyListeners();
  }
}

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

  @override
  Widget build(BuildContext context) {
    final count = context.watch<CartModel>().count;
    return Scaffold(
      appBar: AppBar(
        title: const Text('Coddy Shop'),
        actions: [
          Padding(
            padding: const EdgeInsets.only(right: 8),
            child: IconButton(
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => const CartScreen()),
                );
              },
              icon: Badge(
                isLabelVisible: count > 0,
                label: Text('$count'),
                child: const Icon(Icons.shopping_cart),
              ),
            ),
          ),
        ],
      ),
      body: GridView.count(
        crossAxisCount: 2,
        padding: const EdgeInsets.all(16),
        mainAxisSpacing: 12,
        crossAxisSpacing: 12,
        childAspectRatio: 0.8,
        children: [
          for (Product product in products) ProductCard(product: product),
        ],
      ),
    );
  }
}

class ProductCard extends StatelessWidget {
  const ProductCard({super.key, required this.product});

  final Product product;

  @override
  Widget build(BuildContext context) {
    return Card(
      clipBehavior: Clip.antiAlias,
      child: InkWell(
        onTap: () {
          Navigator.push(
            context,
            MaterialPageRoute(
              builder: (context) => ProductScreen(product: product),
            ),
          );
        },
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Expanded(
              child: Container(
                width: double.infinity,
                alignment: Alignment.center,
                color: product.color.shade50,
                child: Icon(product.icon, size: 56, color: product.color),
              ),
            ),
            Padding(
              padding: const EdgeInsets.all(12),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text(
                    product.name,
                    style: Theme.of(context).textTheme.titleMedium,
                  ),
                  const SizedBox(height: 4),
                  Text(
                    money.format(product.price),
                    style: TextStyle(
                      fontWeight: FontWeight.bold,
                      color: Theme.of(context).colorScheme.primary,
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class ProductScreen extends StatelessWidget {
  const ProductScreen({super.key, required this.product});

  final Product product;

  @override
  Widget build(BuildContext context) {
    final textTheme = Theme.of(context).textTheme;
    return Scaffold(
      appBar: AppBar(title: Text(product.name)),
      body: ListView(
        padding: const EdgeInsets.all(24),
        children: [
          Container(
            height: 240,
            alignment: Alignment.center,
            decoration: BoxDecoration(
              color: product.color.shade50,
              borderRadius: BorderRadius.circular(24),
            ),
            child: Icon(product.icon, size: 120, color: product.color),
          ),
          const SizedBox(height: 24),
          Text(
            money.format(product.price),
            style: textTheme.headlineSmall?.copyWith(
              fontWeight: FontWeight.bold,
              color: Theme.of(context).colorScheme.primary,
            ),
          ),
          const SizedBox(height: 12),
          Text(product.description, style: textTheme.bodyLarge),
          const SizedBox(height: 32),
          FilledButton.icon(
            onPressed: () {
              context.read<CartModel>().add(product);
              ScaffoldMessenger.of(context).hideCurrentSnackBar();
              ScaffoldMessenger.of(context).showSnackBar(
                SnackBar(content: Text('Added ${product.name} to your cart')),
              );
            },
            icon: const Icon(Icons.add_shopping_cart),
            label: const Text('Add to cart'),
          ),
        ],
      ),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    final cart = context.watch<CartModel>();
    return Scaffold(
      appBar: AppBar(title: const Text('Your Cart')),
      bottomNavigationBar: SafeArea(
        child: Padding(
          padding: const EdgeInsets.all(16),
          child: Row(
            children: [
              Text('Total', style: Theme.of(context).textTheme.titleLarge),
              const Spacer(),
              Text(
                money.format(cart.total),
                style: Theme.of(context).textTheme.titleLarge?.copyWith(fontWeight: FontWeight.bold),
              ),
            ],
          ),
        ),
      ),
      body: ListView(
        children: [
          for (Product product in cart.items)
            ListTile(
              leading: CircleAvatar(
                backgroundColor: product.color.shade50,
                child: Icon(product.icon, color: product.color),
              ),
              title: Text(product.name),
              subtitle: Text('${cart.quantityOf(product)} × ${money.format(product.price)}'),
              trailing: Text(money.format(product.price * cart.quantityOf(product))),
            ),
        ],
      ),
    );
  }
}