如何从iphone中的uitextfield中选择文本？

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let textField = UITextField(frame: CGRect(x: 50, y: 100, width: 200, height: 40))
        textField.text = "这是一个示例文本"
        textField.delegate = self
        view.addSubview(textField)
    }
}

extension ViewController: UITextFieldDelegate {
    func textFieldDidBeginEditing(_ textField: UITextField) {
        let startPosition = textField.beginningOfDocument
        let endPosition = textField.endOfDocument
        if let range = textField.textRange(from: startPosition, to: endPosition) {
            textField.selectedTextRange = range
        }
    }
}