Flutter不良状态：流已经听过

Question

我试图在扑朔迷离中使用MethodChannel从本机Android代码接收事件。 即使我设置了AsbroadcastStream（）

接收者

static Stream<dynamic> get accessStream {
  _stream ??= _eventChannel.receiveBroadcastStream().map<dynamic>(
    (event) {
      return MainEvent.fromMap(event);
    },
  );
  return _stream!.asBroadcastStream();
}

。

subs = Receiver.accessStream.listen((event) async {
          if (event != null) {
            events.add(event);
          }
        });

//After Some Time in Cancel Function
await subs.cancel()

但是，一旦我取消流订阅， 第一次，但是当我在app_listen.dart中调用相同功能时。它给出以下错误，

[ +100 ms] E/flutter (32159): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: Bad state: Stream has already been listened to.
[        ] E/flutter (32159): #0      _StreamController._subscribe (dart:async/stream_controller.dart:676:7)
[        ] E/flutter (32159): #1      _ControllerStream._createSubscription (dart:async/stream_controller.dart:827:19)
[        ] E/flutter (32159): #2      _StreamImpl.listen (dart:async/stream_impl.dart:473:9)
[        ] E/flutter (32159): #3      listenEvent(package:trying/util/struct/app_listen.dart:49:51)
[        ] E/flutter (32159): <asynchronous suspension>

感谢您的回答。

Answer 1

我通过删除?? =并用=在receiver.dart中替换它来解决问题。