ViewController没有名为“from”的成员

Question

我正在制作一个程序，该程序接收用户输入的信用卡号并返回信用卡类型。除了当我尝试显示类型时，我已经完成了大部分工作。我一直收到错误ViewController没有名为“from”的成员。你知道问题是什么吗？

@IBAction func CardTypePressed(sender: AnyObject) {

    enum CardType: String {
        case None = "None"
        case Visa = "Visa"
        case AmericanExpress = "American Express"
        case Mastercard = "Mastercard"
        case Discover = "Discover"

        private func regularExpression() -> NSRegularExpression {
            switch self {
            case .Visa:
                return NSRegularExpression(pattern: "^4[0-9]{12}(?:[0-9]{3})?$", options: nil, error: nil)!
            case .AmericanExpress:
                return NSRegularExpression(pattern: "^3[47][0-9]{13}$", options: nil, error: nil)!
            case .Mastercard:
                return NSRegularExpression(pattern: "^5[1-5][0-9]{14}$", options: nil, error: nil)!
            case .Discover:
                return NSRegularExpression(pattern: "^6(?:011|5[0-9]{2})[0-9]{12}$", options: nil, error: nil)!
            default:
                return NSRegularExpression(pattern: ".*", options: nil, error: nil)!
            }
        }
        func isValidFor(cardNumber: String) -> Bool {
            let re = self.regularExpression()
            let range = NSRange(0..<cardNumber.lengthOfBytesUsingEncoding(NSUTF8StringEncoding))
            let matches = re.numberOfMatchesInString(cardNumber, options: nil, range: range)
            return matches > 0
        }

        static let allValues = [Visa, AmericanExpress, Mastercard, Discover]
    }

      func from(cardNumber: String) -> CardType {
        for type in CardType.allValues {
            if type.isValidFor(cardNumber) {
                return type
            }
        }
        return CardType.None
    }
    var creditCardType = self.from(creditCardTextField).rawValue
    typeLabel.text = "Credit Card Type: \(creditCardType)"
}