How to input currency format on a text field (from right to left) using Swift?

Question

I have a number let’s say 0.00.

• When the user taps 1. We should have 0.01
• When the user taps 2. We should display 0.

Answer 1

You can create a currency text field subclassing UITextField. Add a target for UIControlEvents .editingChanged. Add a selector method to filter the digits from your textfield string. After filtering all non digits from your string you can format again your number using NumberFormatter as follow:

Xcode 11.5 • Swift 5.2 or later

import UIKit

class CurrencyField: UITextField {
    var decimal: Decimal { string.decimal / pow(10, Formatter.currency.maximumFractionDigits) }
    var maximum: Decimal = 999_999_999.99
    private var lastValue: String?
    var locale: Locale = .current {
        didSet {
            Formatter.currency.locale = locale
            sendActions(for: .editingChanged)
        }
    }
    override func willMove(toSuperview newSuperview: UIView?) {
        // you can make it a fixed locale currency if needed
        // self.locale = Locale(identifier: "pt_BR") // or "en_US", "fr_FR", etc
        Formatter.currency.locale = locale
        addTarget(self, action: #selector(editingChanged), for: .editingChanged)
        keyboardType = .numberPad
        textAlignment = .right
        sendActions(for: .editingChanged)
    }
    override func deleteBackward() {
        text = string.digits.dropLast().string
        // manually send the editingChanged event
        sendActions(for: .editingChanged)
    }
    @objc func editingChanged() {
        guard decimal <= maximum else {
            text = lastValue
            return
        }
        text = decimal.currency
        lastValue = text
    }
}

---

extension CurrencyField {
    var doubleValue: Double { (decimal as NSDecimalNumber).doubleValue }
}

---

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

---

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

---

private extension Formatter {
    static let currency: NumberFormatter = .init(numberStyle: .currency)
}

---

extension StringProtocol where Self: RangeReplaceableCollection {
    var digits: Self { filter (\.isWholeNumber) }
}

---

extension String {
    var decimal: Decimal { Decimal(string: digits) ?? 0 }
}

---

extension Decimal {
    var currency: String { Formatter.currency.string(for: self) ?? "" }
}

---

extension LosslessStringConvertible {
    var string: String { .init(self) }
}

---

View Controller

class ViewController: UIViewController {

    @IBOutlet weak var currencyField: CurrencyField!
    override func viewDidLoad() {
        super.viewDidLoad()
        currencyField.addTarget(self, action: #selector(currencyFieldChanged), for: .editingChanged)
        currencyField.locale = Locale(identifier: "pt_BR") // or "en_US", "fr_FR", etc
    }
    @objc func currencyFieldChanged() {
        print("currencyField:",currencyField.text!)
        print("decimal:", currencyField.decimal)
        print("doubleValue:",(currencyField.decimal as NSDecimalNumber).doubleValue, terminator: "\n\n")
    }
}

Sample project