//declare this property where it won't go out of scope relative to your listener
let reachability = Reachability()!

reachability.whenReachable = { reachability in
    if reachability.connection == .wifi {
        print("Reachable via WiFi")
    } else {
        print("Reachable via Cellular")
    }
}
reachability.whenUnreachable = { _ in
    print("Not reachable")
}

do {
    try reachability.startNotifier()
} catch {
    print("Unable to start notifier")
}

reachability.stopNotifier()

//declare this property where it won't go out of scope relative to your listener
let reachability = Reachability()!

//declare this inside of viewWillAppear

     NotificationCenter.default.addObserver(self, selector: #selector(reachabilityChanged(note:)), name: .reachabilityChanged, object: reachability)
    do{
      try reachability.startNotifier()
    }catch{
      print("could not start reachability notifier")
    }

@objc func reachabilityChanged(note: Notification) {

  let reachability = note.object as! Reachability

  switch reachability.connection {
  case .wifi:
      print("Reachable via WiFi")
  case .cellular:
      print("Reachable via Cellular")
  case .unavailable:
    print("Network not reachable")
  }
}

reachability.stopNotifier()
NotificationCenter.default.removeObserver(self, name: .reachabilityChanged, object: reachability)