State management: setState, Provider, Riverpod and BLoC

Decide what counts as state, lift it to the right place, and choose between the built-in tools and the three libraries most Flutter teams use.

Where state belongs

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

  @override
  State<CounterPage> createState() => _CounterPageState();
}

class _CounterPageState extends State<CounterPage> {
  int _count = 0;

  void _increment() => setState(() => _count++);

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text('Count: $_count'),
        ElevatedButton(onPressed: _increment, child: const Text('Add')),
      ],
    );
  }
}

The first question is not which library to install, it is whether the state needs to outlive one widget. If it does not, setState is the correct answer and adding a package is overhead.

Sharing with Provider

class CartModel extends ChangeNotifier {
  final _items = <String, int>{};

  Map<String, int> get items => Map.unmodifiable(_items);
  int get totalCount => _items.values.fold(0, (sum, q) => sum + q);

  void add(String sku) {
    _items[sku] = (_items[sku] ?? 0) + 1;
    notifyListeners();
  }
}

// above the widget that needs it
ChangeNotifierProvider(
  create: (_) => CartModel(),
  child: const ShopPage(),
)

// and in a descendant
class CartBadge extends StatelessWidget {
  const CartBadge({super.key});

  @override
  Widget build(BuildContext context) {
    final count = context.select<CartModel, int>((c) => c.totalCount);
    return Badge(label: Text('$count'));
  }
}

• context.watch rebuilds on any change, context.select only when the selected value changes, and context.read never rebuilds.
• Call read inside callbacks and watch inside build; mixing them up is the classic Provider mistake.
• Provide models as high in the tree as the sharing requires and no higher, or every change rebuilds unrelated widgets.

Riverpod and BLoC in practice

final counterProvider = NotifierProvider<Counter, int>(Counter.new);

class Counter extends Notifier<int> {
  @override
  int build() => 0;
  void increment() => state++;
}

// composed and overridable for tests
final greetingProvider = Provider<String>((ref) {
  final n = ref.watch(counterProvider);
  return 'Count is $n';
});

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

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final text = ref.watch(greetingProvider);
    return Text(text);
  }
}

FAQ

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Last refreshed 2026-09-18.