最大字符数以及仅限制UITextField中的数值

class LimitedTextField: UITextField {
    var maxLength: Int = 0
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        self.addTarget(self, action: #selector(textFieldDidChange), for: .editingChanged)
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.addTarget(self, action: #selector(textFieldDidChange), for: .editingChanged)
    }
    
    @objc func textFieldDidChange() {
        guard let text = self.text else { return }
        if text.count > maxLength {
            let endIndex = text.index(text.startIndex, offsetBy: maxLength)
            self.text = String(text[..<endIndex])
        }
    }
}

class ViewController: UIViewController, UITextFieldDelegate {
    @IBOutlet weak var textField: UITextField!
    let maxLength = 10
    
    override func viewDidLoad() {
        super.viewDidLoad()
        textField.delegate = self
    }
    
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        guard let text = textField.text else { return true }
        let newLength = text.count + string.count - range.length
        return newLength <= maxLength
    }
}