如何在 alert.addTextfield 中放置一个 $ 硬币掩码？

Question

如何在alert.addTextfield中放置$硬币掩码？ 货币 ？ 跟textfield有什么关系？ https://code.i-harness.com/en/q/1c673c6

func showalert(with marcas: Marcas?){
    let title = marcas == nil ? "Adicionar" : "Editar"
    let alert = UIAlertController(title: title + " Marca", message: nil, preferredStyle: .alert)
    alert.addTextField { (textField) in textField.placeholder = "Nome da Marca"
        if let name = marcas?.nome {
            textField.text = name

        }
    }
    alert.addTextField { (textFieldValor) in textFieldValor.placeholder = "Preço"
        if let valor = marcas?.valor {
            textFieldValor.text = valor

        }
    }

Answer 1

textFieldValor.addTarget(self, action: #selector(self.myTextFieldDidChange), for: .editingChanged)

 @objc 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 = "R$"
    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)!
}

}