connectivity_状态（28677）：无法关闭现有事件流

2 月，1 周 Questions & Answers 1067

我已经开始在弗利特发展。在一种情况下，我必须检查用户是否连接到互联网。我结合使用connectivity 0.4.9+5和data_connection_checker 0.3.4来检查用户是否有活动连接

我创建了一个文件互联网连接服务。执行与其相关的所有任务的dart

class InternetConnectivityService {
  StreamSubscription<ConnectivityResult> _subscription;

  /*
    * This function check if the device has internet connectivity.
    * With the help of DataConnectionChecker it checks for actual internet connectivity. 
  */
  Future<bool> _checkConnectivity() async {
    if (await DataConnectionChecker().hasConnection) {
      return true;
    } else {
      return false;
    }
  }

  /*
    * This function is invoked to on each connection change request.
    * Using Connectivity package it will check for connectivity and connection type.
    * This function has return type of Future<bool> which perform async request to check connectivity.
    * After checking connection type it check for divice has internet accesssible or not.
  */
  Future<bool> _hasInternet() async {
    var connectivityResult = await (Connectivity().checkConnectivity());
    if (connectivityResult == ConnectivityResult.mobile) {
      return _checkConnectivity();
    } else if (connectivityResult == ConnectivityResult.wifi) {
      return _checkConnectivity();
    } else {
      return false;
    }
  }

  StreamSubscription<ConnectivityResult> initInterNetConnectivitySubscription(
      BuildContext context) {
    // * Subscribe to connectivity changes
    _subscription = Connectivity().onConnectivityChanged.listen(
      (ConnectivityResult result) {
        _hasInternet().then(
          (result) {
            // * When internet is disconnected
            Size size = MediaQuery.of(context).size;
            if (!result) {
              Scaffold.of(context).showSnackBar(
                snackBarBuilder(
                    color: kErrorColor,
                    text: 'Connection Lost',
                    context: context),
              );
            } else {
              Scaffold.of(context).showSnackBar(
                snackBarBuilder(
                    color: kSuccessColor, text: 'Connected', context: context),
              );
            }
          },
        );
      },
    );
    return _subscription;
  }

  disposeSubscription() {
    _subscription.cancel();
  }
}

函数initInterNetConnectivitySubscription和disposeSubscription用于订阅和取消订阅特定事件。我从我想要这个功能的组件调用这些方法

例如：

     InternetConnectivityService internetConnectivityService =
      InternetConnectivityService();

  @override
  initState() {
    internetConnectivityService.initInterNetConnectivitySubscription(context);
    super.initState();
  }

  @override
  dispose() {
    internetConnectivityService.disposeSubscription();
    super.dispose();
  }

通过这样做，功能有时是有效的，但有时我会面临错误声明E/EventChannel#plugins.flutter.io/connectivity_status(28677): Failed to close existing event stream

完成堆栈跟踪

   Restarted application in 5,259ms.
E/EventChannel#plugins.flutter.io/connectivity_status(28677): Failed to close existing event stream
E/EventChannel#plugins.flutter.io/connectivity_status(28677): java.lang.IllegalArgumentException: NetworkCallback was not registered
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at com.安卓.internal.util.Preconditions.checkArgument(Preconditions.java:50)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at 安卓.net.ConnectivityManager.unregisterNetworkCallback(ConnectivityManager.java:4009)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at io.flutter.plugins.connectivity.ConnectivityBroadcastReceiver.onCancel(ConnectivityBroadcastReceiver.java:53)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at io.flutter.plugin.common.EventChannel$IncomingStreamRequestHandler.onListen(EventChannel.java:182)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at io.flutter.plugin.common.EventChannel$IncomingStreamRequestHandler.onMessage(EventChannel.java:167)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:85)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:692)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at 安卓.os.MessageQueue.nativePollOnce(Native Method)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at 安卓.os.MessageQueue.next(MessageQueue.java:336)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at 安卓.os.Looper.loop(Looper.java:174)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at 安卓.app.ActivityThread.main(ActivityThread.java:7356)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at java.lang.reflect.Method.invoke(Native Method)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at com.安卓.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
E/EventChannel#plugins.flutter.io/connectivity_status(28677):   at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:930)**strong text**

由于这个错误，我的应用程序没有崩溃，但有时功能无法正常工作。请让我知道我是否犯了一些错误，或者他们的做法是否更好。我只是不想有这样的功能，当用户并没有连接时，应用程序会显示你们并没有连接到互联网

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java E/EventChannel插件。颤振io/connectivity_状态（28677）：无法关闭现有事件流

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