Class to allow you to use NIB BASED custom UIView in interface builder

NibLoadableView.swift

import UIKit

open class NibLoadableView: UIView {
    //MARK: - Public Properties
    private(set) var customView: UIView!
    
    //MARK: - Lifecycle
    public required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.nibSetup()
        self.initialSetup()
    }
    public override init(frame: CGRect) {
        super.init(frame: frame)
        self.nibSetup()
        self.initialSetup()
    }
    
    //MARK: - Private
    private func nibSetup() {
        customView = loadViewFromNib()
        customView.frame = bounds
        customView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        addSubview(customView)
    }
    private func loadViewFromNib() -> UIView {
        let nib = UINib(nibName: nibName, bundle: bundle)
        return nib.instantiate(withOwner: self, options: nil).first as! UIView
    }
    
    //MARK: - Override Points
    open func initialSetup() { }
    open var nibName: String { return String(describing: self) }
    open var bundle: Bundle { return .main }
}

Usage.swift

//NOTE: By default the .xib has the same name as the class
//      in this instance MyView.xib
//      To use it in interface builder simply add a `UIView` and change its class to `MyView`
//
//      To use a different .xib, override `nibName`

class MyView: NibLoadableView {
    @IBOutlet private var someLabel: UILabel!
    @IBOutlet private var someButon: UIButton!
    
    override func initialSetup() {
        //do one time setup stuff here
        self.backgroundColor = .redColor()
    }
}