collectAsState method

Implementation

ValueNotifier<T> collectAsState(
    {T? initial,
    T Function(Object error, StackTrace stackTrace)? onError,
    Cancellable? cancellable}) {
  ValueNotifier<T>? notifier;

  ValueNotifier<T> createNotifier(T value) {
    if (cancellable == null) {
      return ValueNotifier<T>(value);
    } else {
      return CancellableValueNotifier<T>(value, cancellable);
    }
  }

  late StreamSubscription<T> subscription;

  if (initial != null) {
    notifier = createNotifier(initial);
    subscription = listen((event) {
      notifier!.value = event;
    }, onError: (error, stackTrace) {
      if (onError != null) {
        notifier!.value = onError(error, stackTrace);
      }
    });
  } else {
    subscription = listen((event) {
      if (notifier == null) {
        notifier = createNotifier(event);
      } else {
        notifier!.value = event;
      }
    }, onError: (error, stackTrace) {
      if (onError != null) {
        final value = onError(error, stackTrace);
        if (notifier == null) {
          notifier = createNotifier(value);
        } else {
          notifier!.value = value;
        }
      }
    });
  }

  assert(notifier != null,
      'Stream did not emit any value and no initial value was provided.');

  cancellable?.whenCancel.then((_) => subscription.cancel());

  return notifier as ValueNotifier<T>;
}