BehaviorSubject.isEmpty never finishes when stream is empty

[orestesgaolin]

Consider this case:

  test('test', () async {
    final sub = BehaviorSubject<int>();
    final empty = await sub.isEmpty;
    print(empty);
  });

When run it never finishes.

However, when using .hasValue it works just fine:

  test('test', () async {
    final sub = BehaviorSubject<int>();
    final hasValue = await sub.hasValue;
    print(hasValue);
  });

I wonder if this is a known/expected behavior or bug.

[frankpepermans]

I think you just need to close that BehaviorSubject

[hoc081098]

Stream.isEmpty completes when the Stream emits the first value or done event.

Future<bool> get isEmpty {
  _Future<bool> future = new _Future<bool>();
  StreamSubscription<T> subscription =
      this.listen(null, onError: future._completeError, onDone: () {
    future._complete(true);
  }, cancelOnError: true);
  subscription.onData((_) {
    _cancelAndValue(subscription, future, false);
  });
  return future;
}

Fix:

 test('test', () async {
    final sub = BehaviorSubject<int>();
    sub.close();
    final empty = await sub.isEmpty;
    print(empty);
  });

 test('test', () async {
    final sub = BehaviorSubject<int>();
    sub.add(1);
    final empty = await sub.isEmpty;
    print(empty);
  });