Flutter

Widget Basics

class ProductCard extends StatelessWidget { final Product product; final VoidCallback onTap;

const ProductCard({super.key, required this.product, required this.onTap});

@override Widget build(BuildContext context) { return GestureDetector( onTap: onTap, child: Card( child: Padding( padding: const EdgeInsets.all(16), child: Column( crossAxisAlignment: CrossAxisAlignment.start, children: [ Text(product.name, style: Theme.of(context).textTheme.titleMedium), const SizedBox(height: 4), Text('$${product.price}', style: const TextStyle(color: Colors.grey)), ], ), ), ), ); } }

State Management (Riverpod — recommended)

// Provider definition final productsProvider = FutureProvider<List<Product>>((ref) async { final repo = ref.watch(productRepoProvider); return repo.fetchAll(); });

// Usage in widget class ProductListScreen extends ConsumerWidget { @override Widget build(BuildContext context, WidgetRef ref) { final products = ref.watch(productsProvider);

return products.when(
  data: (items) => ListView.builder(
    itemCount: items.length,
    itemBuilder: (context, i) => ProductCard(product: items[i], onTap: () {}),
  ),
  loading: () => const Center(child: CircularProgressIndicator()),
  error: (err, _) => Center(child: Text('Error: $err')),
);

} }

Navigation (GoRouter)

final router = GoRouter( routes: [ GoRoute(path: '/', builder: (, __) => const HomeScreen()), GoRoute( path: '/product/:id', builder: (, state) => ProductScreen(id: state.pathParameters['id']!), ), ], );

// Navigate context.go('/product/123'); context.push('/product/123'); // pushes onto stack

HTTP Requests (Dio)

final dio = Dio(BaseOptions(baseUrl: 'https://api.example.com'));

dio.interceptors.add(InterceptorsWrapper( onRequest: (options, handler) { options.headers['Authorization'] = 'Bearer $token'; handler.next(options); }, ));

Future<List<Product>> fetchProducts() async { final response = await dio.get('/products'); return (response.data as List).map((e) => Product.fromJson(e)).toList(); }

Platform Channels

// Dart side const channel = MethodChannel('com.example/battery');

Future<int> getBatteryLevel() async { final level = await channel.invokeMethod<int>('getBatteryLevel'); return level ?? -1; }

Anti-Patterns

Anti-Pattern Fix

setState in large widgets Extract state to Riverpod/BLoC

Deeply nested widget trees Extract widgets into separate classes

No const constructors Add const to stateless constructors

String-based navigation Use GoRouter with type-safe routes

No error handling on futures Use .when() or try-catch

Production Checklist

• Release mode builds tested on real devices

• App signing (Android keystore, iOS distribution cert)

• Flavor/scheme setup for dev/staging/prod

• Crashlytics or Sentry integration

• ProGuard rules for Android

• App size optimized (deferred components, tree shaking)

• Accessibility: Semantics widgets used