var manager:CBCentralManager!
 viewDidLoad() { // Or init()
 manager = CBCentralManager()
 manager.delegate = self
 }
func centralManagerDidUpdateState(_ central: CBCentralManager) {
 switch central.state {
 case .poweredOn:
 break
 case .poweredOff:
 print("Bluetooth is Off.")
 break
 case .resetting:
 break
 case .unauthorized:
 break
 case .unsupported:
 break
 case .unknown:
 break
 default:
 break
 }
}