Real-time validation of a textField

If you need to make a field for integer input you can simply subclass UITextField and customize your field within the awakeFromNib method and you can also add there addTarget to UIControlEvents .editingChanged and a method to filter the characters that do not be digits. Here is the response link that I have posted / updated in the OS in English:

import UIKit

class IntegerField: UITextField {
    override func awakeFromNib() {
        super.awakeFromNib()
        addTarget(self, action: #selector(editingChanged), for: .editingChanged)
        keyboardType = .numberPad
        textAlignment = .right
        editingChanged()
    }
    func editingChanged() {
        text = Formatter.decimal.string(from: string.numbers.integer as NSNumber)
    }
}

struct Formatter {
    static let decimal = NumberFormatter(numberStyle: .decimal)
}

extension UITextField {
    var string: String { return text ?? "" }
}

extension String {
    var numbers: String { return components(separatedBy: Numbers.characterSet.inverted).joined() }
    var integer: Int { return Int(numbers) ?? 0 }
}

struct Numbers { static let characterSet = CharacterSet(charactersIn: "0123456789") }

extension NumberFormatter {
    convenience init(numberStyle: NumberFormatter.Style) {
        self.init()
        self.numberStyle = numberStyle
    }
}