iOS 11：蜂窝信号强度

我正在获取如下所述的Cellular Signal Strength（iOS <11），但在iOS 11中，signalStrength始终为0

let statusBarView = UIApplication.shared.value(forKey: "statusBar") as? UIView if let foregroundView = statusBarView?.value(forKey: "foregroundView") as? UIView { let subiews = foregroundView.subviews var dataNetworkItemView:UIView? for subview in subiews { if subview.isKind(of: NSClassFromString("UIStatusBarSignalStrengthItemView")!) == true { dataNetworkItemView = subview break } } var signalStrength = 0 var signalStrengthBars = 0 if let view = dataNetworkItemView { signalStrength = view.value(forKey: "signalStrengthRaw") as! Int signalStrengthBars = view.value(forKey: "signalStrengthBars") as! Int }