如何在ios设备上显示滚动条？

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建UIScrollView实例
        let scrollView = UIScrollView(frame: CGRect(x: 0, y: 0, width: view.frame.width, height: view.frame.height))
        
        // 设置滚动内容的大小
        scrollView.contentSize = CGSize(width: view.frame.width, height: view.frame.height * 2)
        
        // 启用滚动条
        scrollView.showsVerticalScrollIndicator = true
        scrollView.showsHorizontalScrollIndicator = true
        
        // 将UIScrollView添加到视图中
        view.addSubview(scrollView)
    }
}