OTP Code View

Make your own OTP code input view

Posted by Ky Nguyen on April 17, 2018

Two years ago, I did a view for this purpose. Detail is on my github: https://github.com/nguyentruongky/ActiveCode.

It’s 100% code, without auto layout. Today, I make another view, with same purpose, but use auto layout, better UI and much easier to maintain.

UI will be like this.

Initilize view

Init view with number of digits you need and an action to validate your OTP from your controller. The number of digits should be less than 6 for good UI.

Anyone can customize UI themselves for more digits. Digit indicator is • or _ can save more space.

    private var digitCount = 0
    private var validate: ((String) -> Void)?
    convenience init(digitCount: Int, validate: @escaping ((String) -> Void)) {
        self.init(frame: CGRect.zero)
        self.digitCount = digitCount
        self.validate = validate

Setup the UI

    override func setupView() {
        // (1)
        guard digitCount > 0 else { return }

        // (2)
        var constraints = "H:|-8-"
        for i in 0 ..< digitCount {
            let label = makeLabel()
            if i > 0 {
                label.width(toView: labels[0])
            constraints += "[v\(i)]-8-"
        constraints += "|"
        addConstraints(withFormat: constraints, arrayOf: labels)
        // (3)
        setCode(at: 0, active: true)
        addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(becomeFirstResponder)))

    private func makeLabel() -> UILabel {
        let label = knUIMaker.makeLabel(font: UIFont.systemFont(ofSize: 45),
                                    color: color_69_125_245,
                                    alignment: .center)
        // (4)
        label.createBorder(0.5, color: color_102)

        // (5)
        label.vertical(toView: self)
        return label

(1): Prevent code running while no digit. Only support init view by code with init(digitCount:validate), so should prevent other init way to make wrong behaviour.

(2): Set Auto layout code. Create a Visual Format Language string (like this: "H:|-8-[v0]-[v1]-8-|"). Detail is here.

To make sure all digit indicators have same width, I set widthConstraint equal to the first indicator.

(3): Minor stuffs, make first indicator active, set focus to the hiddenTextField to show keyboard.

(4): This is how the indicator look. Want to change UI, just do it here. Please keep the (5) stay here. it is for auto layout setting.

Set hidden UITextField

Just add a UITextField, which is overlapped to use its keyboard and delegate. Every key input, I will update the digit indicator by catch the character in UITextFieldDelegate

    lazy var hiddenTextField = self.addHiddenTextField()
    private func addHiddenTextField() -> UITextField {
        let tf = UITextField()
        tf.translatesAutoresizingMaskIntoConstraints = false
        tf.keyboardType = .numberPad
        tf.isHidden = true
        tf.delegate = self
        addSubviews(views: tf)
        tf.fill(toView: self)
        return tf
    override func becomeFirstResponder() -> Bool {
        return true

Conform UITextFieldDelegate and update method textfield(shouldChangeCharactersIn:replacementString)

    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        var newText = string
        // (1)
        if isInvalid {
            isInvalid = false
        else {
            newText = (textField.text! as NSString).replacingCharacters(in: range, with: string)

        // (2)
        let codeLength = newText.length
        guard codeLength <= digitCount else { return false }
        textField.text = newText
        // (3)
        func setTextToActiveBox() {
            for i in 0 ..< codeLength {
                let char = textField.text!.substring(from: i, to: i)
                labels[i].text = char
                setCode(at: i, active: true)
        // (4)
        func setTextToInactiveBox() {
            for i in codeLength ..< digitCount {
                labels[i].text = ""
                setCode(at: i, active: false)
            if codeLength <= digitCount - 1 {
                setCode(at: codeLength, active: true)
        if codeLength == digitCount {
            validateCode(code: textField.text!)
        return false

(1): Reset all boxes when the code is invalid and type new character.

(2)(3)(4): Update every character from hiddenTextField to every indicator box. Rest of boxes will be set to empty.


The main part is ready. Minors methods, properties are in the lib in github. Link is https://github.com/nguyentruongky/knOtpView.