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NStater — lightweight state management with zero dependencies

NStater is a minimal and fast way to manage state in Flutter. You control the lifecycle of controllers and reactive values yourself, using your own types and subscriptions.

📦 Features

  • NVar — a typed reactive variable that notifies listeners about changes
  • NField — a widget that listens to an NVar and rebuilds only when the value actually changes
  • NController — a base state controller class
  • NState — widget that creates a controller and manages its lifecycle

📦📦 Another Features

  • Custom equality — control when values are considered equal to optimize rebuilds
  • Selective rebuilds — rebuild only when specific parts of state change
  • No dependency on ChangeNotifier/ValueNotifier
  • You can combine multiple NVar or NController instances on a single screen

🔍 Quick API

NVar<T>

Reactive value with subscribe / unsubscribe:

final n = NVar<int>(0);
n.addListener((v) => print('new value: $v'));
// new value: 0
n.value = 42;
print(n.value);
// 42

Custom equality:

// Use custom comparison for complex objects
final items = NVar<List<String>>(
  ['a', 'b'],
  isEqual: (old, new) => ListEquality().equals(old, new),
);
items.value = ['a', 'b']; // Won't notify listeners (content is equal)

NField<T>

A widget that listens to an NVar and rebuilds only when the value actually changes:

NField<int>(
  data: counter,
  builder: (v) => Text('$v'),
);

Selective rebuilds:

class User {
  final String name;
  final int age;
  User(this.name, this.age);
}

final userVar = NVar<User>(User('John', 30));

// Rebuild ONLY when name changes, ignore age updates
NField<User>(
  data: userVar,
  shouldRebuild: (prev, curr) => prev.name != curr.name,
  builder: (user) => Text(user.name),
);

NController

Base controller class with subscriptions and no dependencies:

class CounterController extends NController<CounterController> {
  int count = 0;

  void increment() {
    count++;
    update(); // Notify all listeners
  }

  @override
  void onInit() {
    // Called when widget is created
    print('Controller initialized');
  }

  @override
  void onReady() {
    // Called after first build
    print('Controller ready');
  }

  @override
  void dispose() {
    // Clean up resources
    print('Controller disposed');
    super.dispose();
  }
  
  @override
  void beforeMount() {
    // Call before widget mount, its called before [onInit]
    print('Controller before mount');
    super.beforeMount();
  }
}

NState<C extends NController>

Builds UI based on a controller and automatically creates and disposes it:

NState<CounterController>(
  create: () => CounterController(),
  builder: (controller) => Column(
    children: [
      Text('Count: ${controller.count}'),
      ElevatedButton(
        onPressed: controller.increment,
        child: Text('Increment'),
      ),
    ],
  ),
);

NVarCombiner<R>

Combine multiple NVar sources into a single computed value that automatically updates when any source changes:

final firstName = NVar<String>('John');
final lastName = NVar<String>('Doe');

// Combine two sources
final fullName = NVarCombiner(
  [firstName, lastName],
      () => '${firstName.value} ${lastName.value}',
);

print(fullName.value); // John Doe

firstName.value = 'Jane';
print(fullName.value); // Jane Doe

Form validation example:

final email = NVar<String>('');
final password = NVar<String>('');
final acceptTerms = NVar<bool>(false);

final isFormValid = NVarCombiner(
  [email, password, acceptTerms], () => 
        email.value.contains('@') && 
        password.value.length >= 6 
        && acceptTerms.value,
);

// Use in UI
NField<bool>(
  data: isFormValid,
  builder: (isValid) => ElevatedButton(
    onPressed: isValid ? _submit : null,
    child: Text('Submit'),
  ),
);

⚡ Performance Tips

  1. Use shouldRebuild in NField to prevent unnecessary rebuilds when only specific parts of data change
  2. Use isEqual in NVar for deep equality checks on complex objects (lists, maps)
  3. Dispose resources — always call super.dispose() in controllers and dispose() on NVar instances
  4. Combine multiple NVar — use separate reactive variables for independent state instead of one large object

📚 Lifecycle Methods

NController

  • beforeMount() — called before widget mount
  • onInit() — called when widget is created (analog of initState)
  • onReady() — called after first build is complete
  • dispose() — called when widget is removed from tree

NVar / NVarCombiner

  • dispose() — unsubscribe from all listeners and clean up resources

📄 License

MIT License — see LICENSE file for details.

🤝 Contributing

Issues and pull requests are welcome! Visit GitHub repository.

Libraries

nstater