UITextFieldの入力値を通貨に自動変換

Combineを使うと割とスッキリ実装できる。
今回のサンプルは日本円のみにしてますが、応用して通貨以外にも色々な単位に自動変換するUITextFieldを作れると思います。

class SampleViewController: UIViewController {

    let numberFormatter: NumberFormatter = {
        let nf = NumberFormatter()
        nf.numberStyle = .currency
        nf.locale = Locale(identifier: "ja_JP")
        return nf
    }()

    let textField: UITextField = {
        let tf = UITextField()
        tf.keyboardType = .numberPad
        return tf
    }()

    private var cancellable = Set<AnyCancellable>()

    override func viewDidLoad() {
        super.viewDidLoad()
        textField
            .textDidChangePublisher()
            .map { Int($0.removeCurrencyCharacter()) ?? 0 }
            .map { self.numberFormatter.string(from: NSNumber(value: $0)) }
            .assign(to: \.text, on: textField)
            .store(in: &cancellable)
}

extension UITextField {
    func textDidChangePublisher() -> AnyPublisher<String, Never> {
        NotificationCenter.default
            .publisher(for: UITextField.textDidChangeNotification, object: self)
            .compactMap { ($0.object as? UITextField)?.text }
            .eraseToAnyPublisher()
    }
}

extension String {
    func removeCurrencyCharacter() -> String {
        self.replacingOccurrences(of: ",", with: "")
            .replacingOccurrences(of: "¥", with: "")
    }
}