如何向UITextField添加清除按钮？

import UIKit

class ViewController: UIViewController {

    let textField = UITextField(frame: CGRect(x: 50, y: 100, width: 200, height: 40))

    override func viewDidLoad() {
        super.viewDidLoad()

        textField.borderStyle = .roundedRect
        textField.placeholder = "Enter text here"
        textField.clearButtonMode = .whileEditing

        self.view.addSubview(textField)
    }
}