问异步等待行为不正常

EN

Future mainFn() async {
    print('Listen 1');
    Ob o = await listenFn();
    print('Listen 2');
    return await someFn(o);
  }

Future<Ob> listenFn() async {
    o = new Ob();
    print('Listen 3');
    Stream<Ct> stream = await getCt();
    print('Listen 4');
    stream.listen((Ct _ct) {
      print('Listen 7');
      if (!cts.contains(_ct)) {
        setState(() {
          cts.add(_ct);
        });
      }
    }, onError: (a) {
      print('Listen 8');
      print(a);
    }, onDone: () async {
      print('Listen 9');
      o = await addOb(cts); <-- This function returns Future<Ob>
    });
  await stream.drain();
  print('Listen 14');
  return o;
  }

Future<Stream<Ct>> getCt() async {
  print('Listen 5');
  final String url = 'API_URL';
  final client = new http.Client();
  final request = http.Request('get', Uri.parse(url));
  final streamedRest = await client.send(request);
  print('Listen 6');
  return streamedRest.stream
      .transform(utf8.decoder)
      .transform(json.decoder)
      .map((data) => Helper.getData(data))
      .expand((data) => (data as List))
      .map((data) {
    return Ct.fromJSON(data);
  });
}

I/flutter (22211): Listen 1
I/flutter (22211): Listen 3
I/flutter (22211): Listen 5
I/flutter (22211): Listen 6
I/flutter (22211): Listen 4
I/flutter (22211): Listen 2
I/flutter (22211): Listen 7 <-- 4 Ct items in the stream
I/flutter (22211): Listen 7
I/flutter (22211): Listen 7
I/flutter (22211): Listen 7
I/flutter (22211): Listen 9
I/flutter (22211): Listen 10 <-- added more of these along the way
I/flutter (22211): Listen 11
I/flutter (22211): Listen 12
I/flutter (22211): Listen 13