XibView.swift

//
//  XibView.swift
//  XibView
//
//  Created by Victor Pavlychko on 1/13/18.
//

import UIKit

@IBDesignable
open class XibView: UIView {

    @IBOutlet open var contentView: UIView? {
        didSet {
            guard contentView != oldValue, let contentView = contentView else {
                return
            }
            oldValue?.removeFromSuperview()
            contentView.translatesAutoresizingMaskIntoConstraints = true
            contentView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
            contentView.frame = bounds
            addSubview(contentView)
        }
    }

    public override init(frame: CGRect) {
        super.init(frame: frame)
        instantiateNib(findNib())
    }
    
    public required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        instantiateNib(findNib())
    }
    
    private func findNib() -> (Bundle, String) {
        let superclasses = sequence(first: type(of: self) as AnyClass, next: { return $0.superclass() })
        for cls in superclasses {
            let bundle = Bundle(for: cls)
            let name = String(describing: cls).components(separatedBy: ".").last ?? ""
            if bundle.url(forResource: name, withExtension: "nib") != nil {
                return (bundle, name)
            }
        }
        fatalError("Couldn't find nib for \(type(of: self))")
    }
    
    private func instantiateNib(_ nib: (bundle: Bundle, name: String)) {
        nib.bundle.loadNibNamed(nib.name, owner: self, options: nil)
    }
}