问滚动视图上不显示文本视图

EN

class TeamDetailsController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationController?.navigationBar.prefersLargeTitles = false

        setupViews()
    }

    lazy var scrollView: UIScrollView = {
        let sv = UIScrollView(frame: self.view.bounds)
        sv.backgroundColor = .blue

        sv.autoresizingMask = UIViewAutoresizing(rawValue: UIViewAutoresizing.RawValue(UInt8(UIViewAutoresizing.flexibleWidth.rawValue) | UInt8(UIViewAutoresizing.flexibleHeight.rawValue)))

        sv.contentSize = CGSize(width: self.view.bounds.size.width, height: self.view.bounds.size.height * 2);
        return sv
    }()

    var textView: UITextView = {
        var tv = UITextView()
        tv.textColor = .darkGray
        tv.backgroundColor = .black
        tv.font = UIFont.systemFont(ofSize: 16)
        return tv
    }()

    func setupViews() {

        view.backgroundColor = .white
        view.addSubview(scrollView)            
        scrollView.addSubview(textView)

        scrollView.addConstraintsWithFormat(format: "H:|-16-[v0]-16-|", views: textView)
        scrollView.addConstraintsWithFormat(format: "V:|-16-[v0]-16-|", views: textView)           
    }
}