Flutter: Flutter Introduction and Environment Setup

import 'package:flutter/material.dart';

// One codebase, four platforms
void main() => runApp(const ShopApp());

class ShopApp extends StatelessWidget {
  const ShopApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'ShopApp',
      home: Scaffold(
        appBar: AppBar(title: const Text('ShopApp')),
        body: const Center(child: Text('Hello, Bob!')),
      ),
    );
  }
}

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

import 'package:flutter/material.dart';

class ProductCard extends StatelessWidget {
  final String name;
  final double price;

  const ProductCard({
    super.key,
    required this.name,
    required this.price,
  });

  @override
  Widget build(BuildContext context) {
    return Card(
      child: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(name, style: const TextStyle(fontSize: 18)),
            Text('\$${price.toStringAsFixed(2)}',
                style: const TextStyle(color: Colors.green, fontSize: 16)),
          ],
        ),
      ),
    );
  }
}

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

import 'package:flutter/material.dart';

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

  @override
  State<QuantitySelector> createState() => _QuantitySelectorState();
}

class _QuantitySelectorState extends State<QuantitySelector> {
  int _count = 1;

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        IconButton(
          icon: const Icon(Icons.remove),
          onPressed: () => setState(() => _count = (_count - 1).clamp(1, 99)),
        ),
        Text('$_count', style: const TextStyle(fontSize: 20)),
        IconButton(
          icon: const Icon(Icons.add),
          onPressed: () => setState(() => _count++),
        ),
      ],
    );
  }
}

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

# Add Flutter to PATH in ~/.zshrc or ~/.bashrc
export PATH="$HOME/development/flutter/bin:$PATH"

# Verify installation
flutter --version
# Output: Flutter 3.x.x • channel stable

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

# Run doctor to check all dependencies
flutter doctor

# Expected output:
# [✓] Flutter (Channel stable, 3.x.x)
# [✓] Android toolchain
# [✓] Chrome - develop for the web
# [✓] Android Studio
# [!] VS Code (install Flutter extension)

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

# Create a new Flutter project
flutter create shop_app

# Navigate to project directory
cd shop_app

# Run on connected device or emulator
flutter run

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'ShopApp',
      theme: ThemeData(
        colorSchemeSeed: Colors.blue,
        useMaterial3: true,
      ),
      home: const HomePage(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('ShopApp')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Icon(Icons.shopping_bag, size: 80, color: Colors.blue),
            const SizedBox(height: 16),
            const Text('Welcome to ShopApp!',
                style: TextStyle(fontSize: 24)),
            const SizedBox(height: 8),
            Text('Million-level products, USD settlement',
                style: TextStyle(fontSize: 14, color: Colors.grey[600])),
            const SizedBox(height: 24),
            ElevatedButton(
              onPressed: () {},
              child: const Text('Start Shopping'),
            ),
          ],
        ),
      ),
    );
  }
}

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.

# Start app with hot reload support
flutter run

# After modifying code, press:
# r - Hot reload (keep state, update UI)
# R - Hot restart (reset state, rebuild)
# q - Quit

# Hot reload updates UI in <1 second
# Try: change 'Welcome to ShopApp!' to 'Hello Bob!'
# Press r → UI updates instantly

> Output: Run locally with Flutter SDK (Flutter 3.x / Dart 3.x). The Piston server does not have Flutter installed; use `flutter run` on your local machine for comparison. Actual UI/state may vary slightly across platforms.