UIView awake after

UIView+awakeAfter.swift

import UIKit

extension UIView {

    open override func awakeAfter(using aDecoder: NSCoder) -> Any? {
        let viewType =  type(of: self)
        let nibName = String(describing: Mirror(reflecting: self).subjectType)
        let bundle = Bundle.main //Bundle(for: viewType)

        //Prevents infinite loop from loadNibNamed internally-calling awakeAfterUsingCoder. Is false when called from storyboard, true when
        guard !translatesAutoresizingMaskIntoConstraints
            else { return self }


        guard bundle.path(forResource: nibName, ofType: "nib") != nil,
            let nib = bundle.loadNibNamed(nibName, owner: self, options: nil),
            let replacement = nib.first as? UIView,
            type(of: replacement) == viewType
            else { return self }

        transferProperties(to: replacement)

        let constraints = reparentedConstraints(from: self, to: replacement)

        for sub in subviews {
            let subviewConstraints = sub.reparentedConstraints(from: self, to: replacement)
            sub.removeFromSuperview()
            replacement.insertSubview(sub, at: replacement.subviews.endIndex)
            sub.addConstraints(subviewConstraints)
        }
        replacement.addConstraints(constraints)

        return replacement
    }

    private func reparentedConstraints(from source: UIView, to target: UIView) -> [NSLayoutConstraint] {
        return constraints.map { original in
            let first = source == original.firstItem as? UIView ? target : original.firstItem
            let second = source == original.secondItem as? UIView ? target : original.secondItem
            let constraint = NSLayoutConstraint(
                item: first!,
                attribute: original.firstAttribute,
                relatedBy: original.relation,
                toItem: second,
                attribute: original.secondAttribute,
                multiplier: original.multiplier,
                constant: original.constant)
            constraint.priority = original.priority
            constraint.shouldBeArchived = original.shouldBeArchived
            constraint.identifier = original.identifier
            constraint.isActive = original.isActive

            return constraint
        }
    }

    private func transferProperties(to target: UIView) {
        target.translatesAutoresizingMaskIntoConstraints = false
        target.autoresizingMask = autoresizingMask
        target.isHidden = isHidden
        target.tag = tag
        target.isUserInteractionEnabled = isUserInteractionEnabled
        target.frame = frame
        target.bounds = bounds
        target.clipsToBounds = clipsToBounds
        // Could use better reflection of properties!
    }
}