如何使用Swift在文本字段（从右到左）输入货币格式？

对于 Swift 3 。在文本字段上输入货币格式（从右到左）

override func viewDidLoad() {    super.viewDidLoad()    textField.addTarget(self, action: #selector(myTextFieldDidChange), for: .editingChanged)}func myTextFieldDidChange(_ textField: UITextField) {    if let amountString = textField.text?.currencyInputFormatting() {        textField.text = amountString    }}extension String {    // formatting text for currency textField    func currencyInputFormatting() -> String {        var number: NSNumber!        let formatter = NumberFormatter()        formatter.numberStyle = .currencyAccounting        formatter.currencySymbol = "$"        formatter.maximumFractionDigits = 2        formatter.minimumFractionDigits = 2        var amountWithPrefix = self        // remove from String: "$", ".", ","        let regex = try! NSRegularexpression(pattern: "[^0-9]", options: .caseInsensitive)        amountWithPrefix = regex.stringByReplacingMatches(in: amountWithPrefix, options: NSRegularexpression.MatchingOptions(rawValue: 0), range: NSMakeRange(0, self.characters.count), withTemplate: "")        let double = (amountWithPrefix as NSString).doublevalue        number = NSNumber(value: (double / 100))        // if first number is 0 or all numbers were deleted        guard number != 0 as NSNumber else { return ""        }        return formatter.string(from: number)!    }}