class MyViewController: UIViewController, CardTextFieldDelegate {
	
	@IBOutlet weak var cardTextField: CardTextField?
	
	override func viewDidLoad() {
		cardTextField?.cardTextFieldDelegate = self
		
		...
	}
	
	func cardTextField(_ cardTextField: CardTextField, didEnterCardInformation information: Card, withValidationResult validationResult: CardValidationResult) {
        // A valid card has been entered, if validationResult == CardValidationResult.Valid
    }
    
    func cardTextFieldShouldShowAccessoryImage(_ cardTextField: CardTextField) -> UIImage? {
        // You can return an image which will be used on cardTextField's accessory button
		 // If you return nil but provide an accessory button action, the unicode character "⇤" is displayed instead of an image to indicate an action that affects the text field.
    }
    
    func cardTextFieldShouldProvideAccessoryAction(_ cardTextField: CardTextField) -> (() -> ())? {
		 // You can return a callback function which will be called if a user tapped on cardTextField's accessory button
		 // If you return nil, cardTextField won't display an accessory button at all.
    }
	
	...

// 1. Let your view controller confirm to the CardTextFieldDelegate and CardIOPaymentViewControllerDelegate protocol:
class ViewController: UIViewController, CardTextFieldDelegate, CardIOPaymentViewControllerDelegate {
	...
	
	// MARK: - CardTextFieldDelegate
    func cardTextField(_ cardTextField: CardTextField, didEnterCardInformation information: Card, withValidationResult validationResult: CardValidationResult) {
        if validationResult == .Valid {
        	// A valid payment card has been manually entered or CardIO was used to scan one.
        }
    }
    
    // 2. Optionally provide an image for the CardIO button
    func cardTextFieldShouldShowAccessoryImage(_ cardTextField: CardTextField) -> UIImage? {
        return UIImage(named: "cardIOIcon")
    }
    
    // 3. Set the action for the accessoryButton to open CardIO:
    func cardTextFieldShouldProvideAccessoryAction(_ cardTextField: CardTextField) -> (() -> ())? {
        return { [weak self] _ in
            let cardIOViewController = CardIOPaymentViewController(paymentDelegate: self)
            self?.presentViewController(cardIOViewController, animated: true, completion: nil)
        }
    }
    
    // MARK: - CardIOPaymentViewControllerDelegate
    
    // 4. When receiving payment card information from CardIO, prefill the text field with that information:
    func userDidProvideCreditCardInfo(cardInfo: CardIOCreditCardInfo!, inPaymentViewController paymentViewController: CardIOPaymentViewController!) {
        cardTextField.prefillCardInformation(
        	cardInfo.cardNumber, 
        	month: Int(cardInfo.expiryMonth), 
        	year: Int(cardInfo.expiryYear), 
        	cvc: cardInfo.cvv)
        	
        paymentViewController.dismissViewControllerAnimated(true, completion: nil)
    }
    
    func userDidCancelPaymentViewController(paymentViewController: CardIOPaymentViewController!) {
        paymentViewController.dismissViewControllerAnimated(true, completion: nil)
    }
}

struct MyCardType: CardType {
    
    // MARK: - Required

    // The name of your specified card type:
    public let name = "My Card Type"

    // Note: The image that will be displayed in the card number text field's image view when this card type has been detected will load from an asset with the name `cardType.name`.

    // If the Issuer Identification Number (the first six digits of the entered card number) of a card number 
    // starts with anything from 1000 to 1111, the card is identified as being of type "MyCardType":
    public let identifyingDigits = Set(1000...1111)

    // The number of digits expected in the Card Validation Code.
    public let CVCLength = 4

    // MARK: - Optional

    // The grouping of your card number type. The following results in a card number format
    // like "100 - 0000 - 00000 - 000000":
    // Not specifying this will result in a 16 digit number, separated into 4 groups of 4 digits.
    public let numberGrouping = [3, 4, 5, 6]

    /** 
     A boolean flag that indicates whether CVC validation is required for this card type or not.
     Setting this value to false will hide the CVC text field from the `CardTextField` and remove the required validation routine. The default is true.
     */
    public let requiresCVC = true

    /**
     A boolean flag that indicates whether expiry validation is required for this card type or not.
     Setting this value to false will hide the month and year text field from the `CardTextField` and remove the required
     validation routine. The default is true.
     */
    public let requiresExpiry = true
	
    public init() {
		
    }
}

...

class MyViewController: UIViewController, CardTextFieldDelegate {
	
	@IBOutlet weak var cardTextField: CardTextField?
	...
	
	func viewDidLoad() {
		cardTextField?.cardTypeRegister.registerCardType(MyCardType())
	}
	
	...
}

class ViewController: UIViewController, NumberInputTextFieldDelegate, CardInfoTextFieldDelegate {
    
    @IBOutlet weak var cardNumberTextField: NumberInputTextField!
    @IBOutlet weak var monthInputTextField: MonthInputTextField!
    @IBOutlet weak var yearInputTextField: YearInputTextField!
    @IBOutlet weak var cvcInputTextField: CVCInputTextField!
        
    // A card that is not nil when valid information has been entered in the text fields:
    var card: Card? {
        let number = cardNumberTextField.cardNumber
        let cvc = CVC(rawValue: cvcInputTextField.text ?? "")
        let expiry = Expiry(month: monthInputTextField.text ?? "", year: yearInputTextField.text ?? "")
                        ?? Expiry.invalid
        
        let cardType = cardNumberTextField.cardTypeRegister.cardTypeFor(number: cardNumberTextField.cardNumber)
        if cardType.validate(cvc: cvc).union(cardType.validate(expiry: expiry)).union(cardType.validate(number: number)) == .Valid {
            return Card(number: number, cvc: cvc, expiry: expiry)
        } else {
            return nil
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        cardNumberTextField.numberInputTextFieldDelegate = self
        monthInputTextField.cardInfoTextFieldDelegate = self
        yearInputTextField.cardInfoTextFieldDelegate = self
        cvcInputTextField.cardInfoTextFieldDelegate = self
        
        // Set the `deleteBackwardCallbacks` - closures which are called whenever a user hits
        // backspace on an empty text field.
        monthInputTextField.deleteBackwardCallback = { _ in self.cardNumberTextField.becomeFirstResponder() }
        yearInputTextField.deleteBackwardCallback = { _ in self.monthInputTextField.becomeFirstResponder() }
        cvcInputTextField.deleteBackwardCallback = { _ in self.yearInputTextField.becomeFirstResponder() }
    }
    
    func numberInputTextFieldDidComplete(_ numberInputTextField: NumberInputTextField) {
        cvcInputTextField.cardType = numberInputTextField.cardTypeRegister.cardTypeFor(number: numberInputTextField.cardNumber)
        print("Card number: \(numberInputTextField.cardNumber)")
        print(card)
        monthInputTextField.becomeFirstResponder()
    }
    
    func numberInputTextFieldDidChangeText(_ numberInputTextField: NumberInputTextField) {
        
    }
    
    func textField(_ textField: UITextField, didEnterValidInfo: String) {
        switch textField {
        case is MonthInputTextField:
            print("Month: \(didEnterValidInfo)")
            yearInputTextField.becomeFirstResponder()
        case is YearInputTextField:
            print("Year: \(didEnterValidInfo)")
            cvcInputTextField.becomeFirstResponder()
        case is CVCInputTextField:
            print("CVC: \(didEnterValidInfo)")
        default:
            break
        }
        print(card)
    }
    
    func textField(_ textField: UITextField, didEnterPartiallyValidInfo: String) {
        // The user entered information that is not valid but might become valid on further input.
        // Example: Entering "1" for the CVC is partially valid, while entering "a" is not.
    }
    
    func textField(_ textField: UITextField, didEnterOverflowInfo overFlowDigits: String) {
        // This function is used in a CardTextField to carry digits to the next text field.
        // Example: A user entered "02/20" as expiry and now tries to append "5" to the month.
        //          On a card text field, the year will be replaced with "5" - the overflow digit.
    }
    
    // ...
}