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

For Swift 3. Input currency format on a text field (from right to left)

override func viewDidLoad() {    super.viewDidLoad()    textField.addTarget(self, action: #selector(myTextFieldDidChange), for: .editingChanged)}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 = "$"        formatter.maximumFractionDigits = 2        formatter.minimumFractionDigits = 2        var amountWithPrefix = self        // remove from String: "$", ".", ","        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)!    }}

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 UIKitclass 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

SwiftUI version of this post here

I started with Leo Dabus' answer (which didn't work out of the box for me) and in the process of trying to simplify and make it work ended up with this, which I think is pretty lean & clean if I do say so myself 😎

class CurrencyTextField: UITextField {    /// The numbers that have been entered in the text field    private var enteredNumbers = ""    private var didBackspace = false    var locale: Locale = .current    override init(frame: CGRect) {        super.init(frame: frame)        commonInit()    }    required init?(coder: NSCoder) {        super.init(coder: coder)        commonInit()    }    private func commonInit() {        addTarget(self, action: #selector(editingChanged), for: .editingChanged)    }    override func deleteBackward() {        enteredNumbers = String(enteredNumbers.dropLast())        text = enteredNumbers.asCurrency(locale: locale)        // Call super so that the .editingChanged event gets fired, but we need to handle it differently, so we set the `didBackspace` flag first        didBackspace = true        super.deleteBackward()    }    @objc func editingChanged() {        defer {            didBackspace = false            text = enteredNumbers.asCurrency(locale: locale)        }        guard didBackspace == false else { return }        if let lastEnteredCharacter = text?.last, lastEnteredCharacter.isNumber {            enteredNumbers.append(lastEnteredCharacter)        }    }}private extension Formatter {    static let currency: NumberFormatter = {        let formatter = NumberFormatter()        formatter.numberStyle = .currency        return formatter    }()}private extension String {    func asCurrency(locale: Locale) -> String? {        Formatter.currency.locale = locale        if self.isEmpty {            return Formatter.currency.string(from: NSNumber(value: 0))        } else {            return Formatter.currency.string(from: NSNumber(value: (Double(self) ?? 0) / 100))        }    }}