Subclass of UIView for comfort creating custom views from Xib

CustomXibView.swift

import UIKit

/*
 Usage:
    1. Create new xib file.
    2. Create new swift file containg class subclassed from CustomXibView.
    3. In xib set recently created class name as File's owner.
 */

@IBDesignable
class CustomXibView: UIView {
    var contentView: UIView!

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

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

    // MARK: - Nib handlers
    private func xibSetup() {
        contentView = loadViewFromNib()
        contentView.frame = bounds
        contentView.autoresizingMask = [UIViewAutoresizing.flexibleWidth, UIViewAutoresizing.flexibleHeight]

        addSubview(contentView)
        insertSubview(contentView, at: 0)
    }

    private func loadViewFromNib() -> UIView! {
        let bundle = Bundle(for: type(of: self))
        let nib = UINib(nibName: String(describing: type(of: self)), bundle: bundle)

        return nib.instantiate(withOwner: self, options: nil).first as! UIView
    }

    override func prepareForInterfaceBuilder() {
        super.prepareForInterfaceBuilder()
        xibSetup()
    }
}