override func viewDidLoad() {    super.viewDidLoad()    let context = LAContext()    var error: NSError? = nil    let canEvaluatePolicy = context.canEvaluatePolicy(LAPolicy.deviceOwnerAuthenticationWithBiometrics, error: &error) as Bool    if error != nil {      print(error!.localizedDescription as String)    }    if canEvaluatePolicy {      print("有指紋驗(yàn)證功能")      context.evaluatePolicy(LAPolicy.deviceOwnerAuthenticationWithBiometrics, localizedReason: "放上您的狗爪", reply: { (success: Bool, error: Error?) in        if success {          print("驗(yàn)證成功")        } else {          print("驗(yàn)證失敗: /(error?.localizedDescription)")        }      })    } else {      print("還沒開啟指紋驗(yàn)證呢")    }  }