Shopping Cart: Remove Items

Part of the State Management section of Coddy's Flutter journey. Lesson 26 of 27.

A shopper who adds the wrong thing needs a way back: a delete button on each row of the cart.

The cart can hold the same product twice, so remove by position, not by product. The rule from before still holds: never change state in place. Make a copy, change the copy, and set it as the new state:

void removeAt(int index) {
  final copy = [...state];
  copy.removeAt(index);
  state = copy;
}

To know each row's position, loop with an index: for (var i = 0; i < cart.length; i++), and use cart[i] for the product in that row.

Delete an item and watch the rest follow: the list, the total and, back on the shop, the badge. They all watch the same cart.

Challenge

Hard

On the cart screen:

Add a removeAt(int index) method to Cart that sets a new list without that item.
Move each row's price to subtitle, and make trailing an IconButton with Icons.delete that removes that row.

Try it yourself

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

class Product {
  const Product(this.name, this.price);

  final String name;
  final double price;
}

const products = [
  Product('Apple', 0.5),
  Product('Bread', 2.25),
  Product('Cheese', 4),
  Product('Milk', 1.2),
];

class Cart extends Notifier<List<Product>> {
  @override
  List<Product> build() => [];

  void add(Product product) {
    state = [...state, product];
  }
}

final cartProvider = NotifierProvider<Cart, List<Product>>(Cart.new);

final totalProvider = Provider((ref) {
  final cart = ref.watch(cartProvider);
  return cart.fold(0.0, (sum, product) => sum + product.price);
});

void main() {
  runApp(const ProviderScope(child: MyApp()));
}

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

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

class ShopPage extends ConsumerWidget {
  const ShopPage({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final cart = ref.watch(cartProvider);
    return Scaffold(
      appBar: AppBar(
        title: const Text('Shop'),
        actions: [
          IconButton(
            icon: Badge(
              label: Text('${cart.length}'),
              isLabelVisible: cart.isNotEmpty,
              child: const Icon(Icons.shopping_cart),
            ),
            onPressed: () {
              Navigator.push(
                context,
                MaterialPageRoute(builder: (context) => const CartScreen()),
              );
            },
          ),
        ],
      ),
      body: ListView(
        children: [
          for (final product in products)
            ListTile(
              title: Text(product.name),
              subtitle: Text('\$${product.price.toStringAsFixed(2)}'),
              trailing: IconButton(
                icon: const Icon(Icons.add_shopping_cart),
                onPressed: () {
                  ref.read(cartProvider.notifier).add(product);
                },
              ),
            ),
        ],
      ),
    );
  }
}

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

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final cart = ref.watch(cartProvider);
    final total = ref.watch(totalProvider);
    return Scaffold(
      appBar: AppBar(title: const Text('Your cart')),
      bottomNavigationBar: Padding(
        padding: const EdgeInsets.all(24),
        child: Text(
          'Total: \$${total.toStringAsFixed(2)}',
          style: const TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
        ),
      ),
      body: cart.isEmpty
          ? const Center(child: Text('Your cart is empty'))
          : ListView(
              children: [
                for (final product in cart)
                  ListTile(
                    title: Text(product.name),
                    trailing: Text('\$${product.price.toStringAsFixed(2)}'),
                  ),
              ],
            ),
    );
  }
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

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