Maximum limit of a text box - Swift

Set the delegate of UITextField to an object of your own and implements the textField shouldChangeCharactersInRange method.

Example:

class ViewController: UIViewController, UITextFieldDelegate {

    let maxCharCount = 3

    @IBOutlet weak var textField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        self.textField.delegate = self
    }

    func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
        return textField.text!.characters.count + string.characters.count <= self.maxCharCount
    }
}

This code does not address the case of the user pasting text into the textfield that goes beyond the maximum number (the way it is, it will not), but you can already have an idea how to do it.

You can create your own text box by subclassing the UITextField as follows:

@IBDesignable
class LimitedLengthField: UITextField {
    @IBInspectable var maxLength: Int = 3 // determine o limite máximo de characters para a sua caixa de texto
    var stringValue: String { return text ?? "" }
    override func awakeFromNib() {
        super.awakeFromNib()
        keyboardType = .ASCIICapable   // escolha o teclado padrao para a sua caixa de texto
        addTarget(self, action: #selector(editingChanged), forControlEvents: .EditingChanged)
        editingChanged(self)
    }
    func editingChanged(sender: UITextField) {
        sender.text = String(stringValue.characters.prefix(maxLength))
    }
}