自定义 UIView 类约束取决于 ParentView

我正在制作一个包含日期选择器的自定义 UIView 类。我想设置视图约束以引用将调用我的自定义类的父视图。这是我的以下代码。这就是我得到的线程 1：致命错误：在展开可选值时意外发现 nil

class CustomView: UIView {
    var datepicker:UIDatePicker!
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupConstraints()
    } // initiliaze the button like this CustomButton()

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

    }

    func setupDatePicker() {
        let datepicker = UIDatePicker()
        datepicker.minimumDate = Date()
    }

    func setupConstraints(){
        setupDatePicker()

        translatesAutoresizingMaskIntoConstraints = false
        leadingAnchor.constraint(equalTo: superview!.leadingAnchor, constant: 20).isActive = true // the error occurs here
        trailingAnchor.constraint(equalTo: superview!.trailingAnchor, constant: -20).isActive = true
        heightAnchor.constraint(equalToConstant: 60).isActive = true
        centerYAnchor.constraint(equalTo: superview!.centerYAnchor).isActive = true
        backgroundColor = .red


        addSubview(datepicker)
        datepicker.translatesAutoresizingMaskIntoConstraints = false
        datepicker.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 10).isActive = true
        datepicker.trailingAnchor.constraint(equalTo: self.trailingAnchor, constant: -10).isActive = true
        datepicker.heightAnchor.constraint(equalToConstant: 50).isActive = true
        datepicker.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true



    }


}

这是我创建自定义视图并启动它的地方

    var customView: CustomView!

class ListViewController: UIViewController {
    @IBOutlet var tableView: UITableView!

    override func viewDidLoad() {
            super.viewDidLoad()
         customView = CustomView()
         view.addSubview(customView)
         view.bringSubviewToFront(customView)

感谢您的时间。