如何在UITextField中允许退格？

class ViewController: UIViewController, UITextFieldDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let textField = UITextField(frame: CGRect(x: 50, y: 50, width: 200, height: 30))
        textField.borderStyle = .roundedRect
        textField.delegate = self
        self.view.addSubview(textField)
    }
    
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        // 判断是否按下了退格键
        if string.isEmpty {
            // 执行退格操作，例如删除最后一个字符
            let currentText = textField.text ?? ""
            let updatedText = String(currentText.dropLast())
            textField.text = updatedText
        }
        
        // 允许其他字符的输入
        return true
    }
}