iOSでよく扱う入力制限についての備忘録です

@IBOutlet private weak var quantityTextField: UITextField!

override func viewDidLoad() {
        super.viewDidLoad()

        quantityTextField.delegate = self
}

//省略

extension ViewController: UITextFieldDelegate {
    
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        
        guard let text = textField.text else {
            return false
        }
        
        if textField === quantityTextField {
            //数値のみチェック
            guard string.isEmpty || !string.match(#"^\d+$"#).isEmpty else {
                return false
            }
            //レンジを取得
            guard let textRange = Range(range, in: text) else {
                return false
            }
            // `textRange`の範囲をstringへ置換
            let updatedText = text.replacingCharacters(in: textRange, with: string)
            //桁数チェック
            guard
                updatedText.count < 6 else {
                return false
            }
            //最初に0は拒否
            guard updatedText.match(#"^0"#).isEmpty else {
                return false
            }
        }
        
        return true
    }
    
}

正規表現を扱うのでStringクラスを拡張

extension String {
    func match(_ pattern: String) -> [String] {
        guard let regex = try? NSRegularExpression(pattern: pattern),
              let matched = regex.firstMatch(in: self, range: NSRange(location: 0, length: self.count))
        else { return [] }
        return (0 ..< matched.numberOfRanges).map {
            NSString(string: self).substring(with: matched.range(at: $0))
        }
    }
}

おかしいところがもしあれば教えてください🙇‍♂️