使用自动约束将视图居中-Swift

我正在创建XIB / datePicker类，当用户点击按钮时，将通过调用viewController以编程方式调用它。如何使用自动约束将该视图放置在调用按钮的正下方并与之对齐。我的代码可以纵向运行，但是在旋转设备时会失败（datePicker不会重新居中）。可能是因为我将CGRect作为视图init的参数传递了，但旋转时并没有改变。我看不到任何其他替代CGRect传递的方法。当我添加自动约束代码时，会出现运行时自动格式化错误。

ViewController：

@IBAction func showMyDatePicker(_ sender: Any) {
    showMyDatePicker.isEnabled = false
    let today = Date()
    let minDate = Calendar.current.date(byAdding: .month, value: -3, to: today)
    let maxDate = Calendar.current.date(byAdding: .month, value: 3, to: today)

    let datePickerWidth = 300
    let datePickerHeight = 200

    let datePickerX = Int(showMyDatePicker.center.x - CGFloat(datePickerWidth / 2))
    let datePickerY = Int(showMyDatePicker.center.y + CGFloat(showMyDatePicker.bounds.height / 2))
    let frame = CGRect(x: datePickerX, y: datePickerY, width: datePickerWidth, height: datePickerHeight)

    myDatePicker = MyDatePicker(frame: frame)
    myDatePicker?.setMyDatePicker(date: today, minimumDate: minDate!, maximumDate: maxDate!)
    myDatePicker?.delegate = self
    self.view.addSubview(myDatePicker!)

}

datePickerClass：

class MyDatePicker: UIView {

var delegate: MyDatePickerDelegate?

@IBOutlet var contentView: UIView!

@IBOutlet weak var datePicker: UIDatePicker!
@IBOutlet weak var returnButton: UIButton!

@IBAction func datePickerChanged(_ sender: Any) {
    delegate?.dateFromDatePicker(date: datePicker.date, closeDatePickerView: false)
}

@IBAction func returnButtonTapped(_ sender: Any) {
    delegate?.dateFromDatePicker(date: datePicker.date, closeDatePickerView: true)
}

override init(frame: CGRect) {
    super.init(frame: frame)
    initView()
}

required init?(coder: NSCoder) {
    super.init(coder: coder)
    initView()
}

private func initView() {//QUESTION: how can I set the datepicker initial values within here
    // Instantiate the view from xib file
    let contentView = Bundle.main.loadNibNamed("MyDatePicker", owner: self, options: nil)?.first as? UIView

    // Check that it's not nil
    guard contentView != nil else {
        return
    }

    // Add the view and set its frame
    addSubview(contentView!)
    contentView?.frame = self.bounds
    contentView?.autoresizingMask = [.flexibleHeight, .flexibleWidth]
}


func setMyDatePicker(date: Date, minimumDate: Date, maximumDate: Date) {
    datePicker.date = date
    datePicker.minimumDate = minimumDate
    datePicker.maximumDate = maximumDate
}

}