Flutter Await Callback Not Give Any Response - dart

Question

I am still a beginner on dart flutter, now I am trying to retrieve data from the REST API and socket.IO. at this time I have a confusing problem, I have tried searching on the internet for 3 days, but there is no solution. I have async and await scripts, but the function I added await doesn't give any response and still pause.
it is assumed that I have two different files, the first is the main file and the second is the helper file.
main.dart
Future<List<ChatTile>> fetchChat(socketutil,id) async {
socketutil.join(id); //STACK IN HERE
SharedPreferences prefs = await SharedPreferences.getInstance();
String messagePrefs = prefs.getString('messagePrefs');
print("DUA");
return await compute(parseListChat, messagePrefs);
}
helper.dart
Future<void> join(String id_room) async {
String jsonData ='{"room_id" : "$id_room","user_id" : "5a91687811138e74009839c9","user_name" : "Denis Muhammad Ramdan","user_photo" : "photo.jpg","user_status" : "1"}';
socketIO.sendMessage("join", jsonData, null);
//subscribe event
return await socketIO.subscribe("updateMessageList", (result) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
await prefs.setString('messagePrefs', result);
print('SATU');
return await result;
});
}
my question is there something wrong with my code, and how is the best way?
many thanks,

Answer 1

I suggest you to add await_only_futures to your analyzer config
analysis_options.yaml
lint:
rules:
- await_only_futures
You also don't need to do return await something since your function already return a future, this is redondant.
And from what I see of the socketio subscribe method, it does not return the result like you expect but use a callback and does not return it (https://pub.dartlang.org/documentation/flutter_socket_io/latest/flutter_socket_io/SocketIO/subscribe.html)
to handle this you should use a Completer
final completer = Completer<String>()
socketIO.subscribe("updateMessageList", (result) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
await prefs.setString('messagePrefs', result);
socketIO.unSubscribe("updateMessageList");
completer.complete(result);
});
return completer.future;
you probably want to handle error when there is using completer.completeError(error)
Update
You can alos convert the subscription to a Dart Stream to handle more case.
StreamController<String> controller;
Stream<String> get onUpdateMessageList {
if (controller != null) return controller.stream;
constroller = StreamController<String>.broadcast(
onCancel: () => socketIO.unSubscribe("updateMessageList"),
);
socketIO.subscribe("updateMessageList", constroller.add);
return controller.stream;
}
Future<StreamSubscription> join(String id_room) async {
...
return onUpdateMessageList.listen((result) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
await prefs.setString('messagePrefs', result);
});
}