使用闭包的 Dart 过滤流列表

Question

I have a list of firestore records as stream. I want to pass uid of a record to the list and return next item.

uid     name
-----|-------------
001  | Steve
002  | David
003  | Mark
004  | George
-------------------

If I pass uid 001 the method should return 002 | David and passing 001 or 004 should return null.

class SearchResultsBloc implements BlocBase {
  SearchResultsBloc() {
    DatabaseService().Search().listen((data) => _inList.add(data));
  }

  final _listController = BehaviorSubject<List<Profile>>();
  Stream<List<Profile>> get outList => _listController.stream;
  Sink<List<Profile>> get _inList => _listController.sink;

  Stream<Profile> nextProfile(String uid) {
    var id = outList
        .map<int>(
            (results) => results.indexWhere((profile) => profile.uid == uid))
        .first;

    Stream<Profile> profile = id.then((index) {
      return outList.map<Profile>((results) => results.elementAt(index));
    });

    return profile;
  }


  @override
  void dispose() {
    _listController.close();
  }
}

I've tried this code but it's throwing error.

A value of type 'Future<Stream<Profile>>' can't be assigned to a variable of type 'Stream<Profile>'.

  Stream<Profile> nextProfile(String uid) {
    var id = outList
        .map<int>(
            (results) => results.indexWhere((profile) => profile.uid == uid))
        .first;

    Stream<Profile> profile = id.then((index) {
      return outList.map<Profile>((results) => results.elementAt(index));
    });

    return profile;
  }

Answer 1

Okay, this seems to work. Not sure whether this is the best solution.

 Stream<Profile> nextProfile(String uid) {
    var index = outList
        .map<int>(
            (results) => results.indexWhere((profile) => profile.uid == uid))
        .first
        .asStream();

    int nextIndex;
    index.listen((index) {
      nextIndex = index + 1;
    });

    return outList.map<Profile>((results) => results.elementAt(nextIndex));
  }