MSAV_snippet4.swift

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

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

    func initView() {
        // Step 1
        guard let xibItems = Bundle.main.loadNibNamed("ListingView", owner: self, options: nil), let firstXibView = xibItems[0] as? UIView else {
            fatalError("Xib is empty or first view is not a UIView")
        }
        // Step 2
        firstXibView.translatesAutoresizingMaskIntoConstraints = false
        
        // Step 3
        let viewConstraints = [NSLayoutAttribute.top, NSLayoutAttribute.left, NSLayoutAttribute.bottom, NSLayoutAttribute.right].map { (attribute) -> NSLayoutConstraint in
            return NSLayoutConstraint(item: firstXibView, attribute: attribute, relatedBy: .equal, toItem: self, attribute: attribute, multiplier: 1, constant: 0)
        }
        
        // Step 4
        addSubview(firstXibView)
        addConstraints(viewConstraints)
    }
}