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("有指纹验证功能")
      context.evaluatePolicy(LAPolicy.deviceOwnerAuthenticationWithBiometrics, localizedReason: "放上您的狗爪", reply: { (success: Bool, error: Error?) in
        if success {
          print("验证成功")
        } else {
          print("验证失败: \(error?.localizedDescription)")
        }
      })
    } else {
      print("还没开启指纹验证呢")
    }
  }