Flutter：捕获Firebase消息传递连接

Question

我在flutter应用程序中实现了fiebase消息传递。我正在尝试捕获连接错误，例如：

6.26.0 - [Firebase/Messaging][I-FCM002025] Failed to connect to direct channel, error: Error Domain=com.google.fcm Code=4 "No internet available, cannot connect to FIRMessaging" UserInfo={NSLocalizedFailureReason=No internet available, cannot connect to FIRMessaging}

但是没有地方可以抓住它。如何捕获Firebase消息传递连接？

final FirebaseMessaging _fcm = FirebaseMessaging();
    _fcm.getToken().then((value) {
      _token = value;
      print("Message token is: $_token");
    }, onError: (err) {
      print("getToken onError is: $err");
    }).catchError((onError) {
      print("getToken catchError is: $onError");
    });