UISegmentedControl选择的索引总是0？

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let segmentedControl = UISegmentedControl(items: ["选项1", "选项2", "选项3"])
        segmentedControl.frame = CGRect(x: 50, y: 100, width: 200, height: 50)
        segmentedControl.selectedSegmentIndex = 0
        segmentedControl.addTarget(self, action: #selector(segmentedControlValueChanged(_:)), for: .valueChanged)
        self.view.addSubview(segmentedControl)
    }

    @objc func segmentedControlValueChanged(_ sender: UISegmentedControl) {
        let selectedIndex = sender.selectedSegmentIndex
        print("选中的索引值为：\(selectedIndex)")
    }
}