Advanced Usage

This page covers advanced features of neat_state for global observability and action interception.

NeatObserver

NeatObserver allows you to listen to events across all NeatNotifier instances in your app. This is useful for logging, analytics, or debugging.

To use it, implement the NeatObserver interface and assign it to NeatNotifier.observer.

class MyLogger extends NeatObserver {
  @override
  void onAction(NeatNotifier notifier, dynamic action) {
    print('[Action] ${notifier.runtimeType}: $action');
  }

  @override
  void onStateChange(NeatNotifier notifier, dynamic state) {
    print('[State] ${notifier.runtimeType}: $state');
  }

  @override
  void onError(NeatNotifier notifier, Object error, StackTrace? stackTrace) {
    print('[Error] ${notifier.runtimeType}: $error');
  }
}

void main() {
  NeatNotifier.observer = MyLogger();
  runApp(MyApp());
}

Interceptors

Interceptors allow you to inspect, transform, or block actions before they are emitted to listeners.

Each NeatNotifier has an interceptors list. You can add functions to this list. - Return the action (modified or original) to pass it to the next interceptor. - Return null to block the action.

class AuthNotifier extends NeatNotifier<AuthState, AuthAction> {
  AuthNotifier() : super(AuthState.initial()) {
    // Add an interceptor
    interceptors.add((action) {
      if (action is NavigateHome && !value.isAuthenticated) {
        // Block navigation if not authenticated
        return null; 
      }
      return action;
    });
  }
}