swift UIView中嵌入UIScrollview滚动

class ViewController: UIViewController {
    var scroll:UIScrollView?
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let root = UIView.init(frame: CGRect.init(x: 0, y: 300, width: self.view.bounds.width, height: 200))
        root.backgroundColor = .gray
        
        scroll = UIScrollView.init(frame: root.bounds)
        
        for i in 0...10 {
            let lab = UILabel.init(frame: CGRect.init(x: 0, y: 100 * i, width: Int(self.view.bounds.width), height: 100))
            lab.text = "lab\(i)"
            scroll?.addSubview(lab)
        }

        scroll?.contentSize  = CGSize.init(width: self.view.bounds.size.width, height: 100 * 11)
        
        root.addSubview(scroll!)
        self.view.addSubview(root)
    }

}