问如何在iOS项目中正确实现条带？

EN

import UIKit

class PaymentInfoController: UIViewController {


@IBOutlet weak var paymentLabel: UILabel!
@IBOutlet weak var cardField: UITextField!
@IBOutlet weak var cvcField: UITextField!
@IBOutlet weak var expField: UITextField! 

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {   

    if let checkoutVC = segue.destination as? CheckoutController {
        checkoutVC.cardNumber = self.cardField.text!
        checkoutVC.cvc = self.cvcField.text!

        if self.expField.text?.isEmpty == false {

            expField.text?.contains("0123456789/")
            (expField.text?.characters.count)! <= 7
        let expDate = self.expField.text?.components(separatedBy: "/")
        let expMonth = UInt((expDate?[0])!)
        let expYear = UInt((expDate?[1])!)

        checkoutVC.expMon = expMonth!
        checkoutVC.expYear = expYear!
        }
    }
}

@IBAction func checkout(_ sender: Any) {
    performSegue(withIdentifier: "checkout", sender: self)  
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
}

import UIKit
import FirebaseAuth
import FirebaseDatabase
import Firebase
import Stripe

    class CheckoutController: UIViewController {

    let ref = Database.database().reference()

    @IBOutlet weak var feeLabel: UILabel!
    @IBOutlet weak var amountLabel: UILabel!

    var cardNumber = String()
    var cvc = String()
    var expMon = UInt()
    var expYear = UInt()

    @IBAction func purchase(_ sender: Any) {

        if Auth.auth().currentUser != nil {

            // Initiate the card
            let stripCard = STPCard()

            STPAPIClient.shared().createToken(withCard: stripCard, completion: { (token, error) -> Void in

                if error != nil {

                    print("There is an error")
                } 

                else {

                    // Send the card info to Strip to get the token
                    stripCard.number = self.cardNumber
                    stripCard.cvc = self.cvc
                    stripCard.expMonth = UInt(self.expMon)
                    stripCard.expYear = UInt(self.expYear)

                    let alert = UIAlertController(title: "Your Stripe token is " + (token?.tokenId)!, message: "", preferredStyle: .alert)
                    let defaultAction = UIAlertAction(title: "OK", style: .default, handler: nil)
                    alert.addAction(defaultAction)
                    self.present(alert, animated: true, completion: nil)
                    print(token!)
                }
            })

        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

    let user = Auth.auth().currentUser
        let userID: String = (user?.uid)!

        if user != nil {

      let totalRef = ref.child("users/\(userID)").child("Total")
          totalRef.observeSingleEvent(of: .value, with: { (snapshot) in
            let cost = snapshot.value as! Int
            self.totalLabel.text = "\(cost) bookies"

            let total = (Double(cost) * 1.35) + 1.39

            self.amountLabel.text = "$\(total)"
        }) 
    }
}