Bloc: Unhandled Exception: 'package:bloc/src/transition.dart': Failed assertion: nextState != null': is not true

[wxy520ll]

my code as below(report error)

 @override
  Stream<String> mapEventToState(Map event)async* {
    Future<String> f = request1(event);
    yield* f.asStream();
  }
  Future<String> request1(Map m) async {
    //rxdart+dio  request data
    var header = {
      "Authorization": "Basic d2ViQXBwOndlYkFwcA==",
    };
    Observable<Response<String>>response= await   Observable(Dio()
          .post<String>("http://******:30099//zuul/api-auth/oauth/token",
              queryParameters: m, options: Options(headers: header))
          .asStream());
    response.listen((rs) {
      if (rs.statusCode == 200) {
        print("success");
        return Future.value("1111");
      } else {
        print("error");
        return Future.value("22222");
      }
    });

i don't kown when i set listen,the code report exception

and other way (right)

Response<String> rs = await Dio().post<String>(
          "http://*****:30099//zuul/api-auth/oauth/token",
          queryParameters: m,
          options: Options(headers: header));
      print("done");
      if (rs.statusCode == 200) {
        print("success");
        return Future.value(rs.data);
      } else {
        print("error");
        return Future.value("error");
      }

[felangel]

Hi @wxy520ll 👋
Thanks for opening an issue!

Just to clarify, the second way works fine and the first way throws an exception?
In general, I would not recommend subscribing to streams within mapEventToState because you block the event loop. Instead, I would recommend subscribing to whatever stream you have in the bloc's constructor and dispatching events in response to new data. Check out this example.

Hope that helps! 👍

[wxy520ll]

thank you very much