State Management

flutter pub add provider

// Counter with setState (local)
class CounterScreen extends StatefulWidget {
  const CounterScreen({super.key});
  @override State<CounterScreen> createState() => _CounterScreenState();
}

class _CounterScreenState extends State<CounterScreen> {
  int _count = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Counter')),
      body: Center(
        child: Text('$_count', style: const TextStyle(fontSize: 48)),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => setState(() => _count++),
        child: const Icon(Icons.add),
      ),
    );
  }
}

// Provider pattern — shared state
// lib/providers/cart_provider.dart
import 'package:flutter/foundation.dart';

class CartProvider extends ChangeNotifier {
  final List<String> _items = [];
  List<String> get items => List.unmodifiable(_items);

  void add(String item) {
    _items.add(item);
    notifyListeners(); // rebuilds listening widgets
  }
}

// main.dart — wrap app
ChangeNotifierProvider(
  create: (_) => CartProvider(),
  child: const MyApp(),
)

// Any widget
final cart = context.watch<CartProvider>();
// or read without rebuilding:
context.read<CartProvider>().add('Apple');