SelectValueNotifier

select_value_notifier.dart

class _SelectValueNotifier<R, T> extends ValueNotifier<R> {
  _SelectValueNotifier(this.source, this.selector)
      : super(selector(source.value)) {
    source.addListener(_sourceListener);
  }

  final ValueNotifier<T> source;
  final R Function(T value) selector;

  void _sourceListener() => value = selector(source.value);

  @override
  void dispose() {
    source.removeListener(_sourceListener);
    super.dispose();
  }
}

extension SelectValueNotifier<T> on ValueNotifier<T> {
  ValueNotifier<R> select<R>(R Function(T value) selector) =>
      _SelectValueNotifier<R, T>(this, selector);
}

Usage:

final car = Car(id: 1, name: 'Honda');
final carNotifier = ValueNotifier(car);
final carNameNotifier = carNotifier.select((car) => car.name);

carNameNotifier.addListener(() {
  print('Car name: ${carNameNotifier.value}');
});

OR

ValueListenableBuilder(
  valueListenable: carNotifier.select((car) => car.name),
  builder: (BuildContext context, value, Widget? child) {
     return Text('Car name: $value);
  }
)