商店：商品详情

本课属于 Coddy Flutter 学习旅程的“项目”单元。第 21 课，共 36 课。

在商店里点按一个商品，就会打开它的页面：一张大图、价格和几句商品介绍。这是第二个屏幕，ProductScreen，它通过构造函数接收商品。

要让整张卡片都能点按，请将 InkWell 放在 Card 内部，包住卡片内容。它会运行 onTap，并绘制你在 Material 应用中看到的水波纹；卡片的 Clip.antiAlias 会将水波纹限制在圆角内。

Card(
  clipBehavior: Clip.antiAlias,
  child: InkWell(
    onTap: () {
      Navigator.push(context, MaterialPageRoute(
        builder: (context) => ProductScreen(product: product),
      ));
    },
    child: Column(...),
  ),
)

商品页面使用 ListView，因此较长的商品介绍可以滚动查看。它的 AppBar 会显示商品名称和返回箭头。Flutter 会在你推入的新屏幕上自动添加返回箭头。

要显示醒目的大号价格，请从主题的 headlineSmall 开始，并使用 copyWith 只修改需要的内容：textTheme.headlineSmall?.copyWith(fontWeight: FontWeight.bold)。这里使用 ?.，是因为主题样式可能为 null。

挑战

中等

为每个商品创建一个页面：

编写一个 ProductScreen，接收一个 required 的 product，并在其 AppBar 中显示商品名称
页面主体是一个 ListView，内边距为 24 像素：先放置一个高 240 像素的卡片，颜色为 product.color.shade50，圆角为 24，图标大小为 120；然后留出 24 像素间距，显示价格（使用主色的粗体 headlineSmall），再留出 12 像素间距，显示 bodyLarge 样式的描述
用 InkWell 包裹每张卡片的 Column，点击后跳转到对应商品的页面

亲手试试

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

void main() {
  runApp(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 ShopScreen extends StatelessWidget {
  const ShopScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Coddy Shop')),
      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: 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,
                  ),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}