Designable XIB. Set XIB's owner to ViewName, connect top view to ViewName.view outlet

swift

final class ViewName: UIView {
    @IBOutlet weak var view: UIView!

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

        setupView()
    }

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

        setupView()
    }

    override func awakeFromNib() {
        super.awakeFromNib()
    }

    private func setupView() {
        let bundle = Bundle(for: type(of: self))
        UINib(nibName: "DetailedDropdownView", bundle: bundle) //xib name
            .instantiate(withOwner: self, options: nil)

        addSubview(self.view)
        self.view.frame = bounds
    }
}