@IBDesignable view that wraps & renders views from nib files

NibWrapperView.swift

//
//  NibWrapperView.swift
//
//  Created by Alek Åström on 2016-01-13.
//  http://github.com/mralek
//
//  Copyright © 2016 Alek Åström
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.


import UIKit

@IBDesignable public class NibWrapperView: UIView {
    
    @IBInspectable public var nibName: String? = nil {
        didSet {
            guard nibName != oldValue else {
                return
            }

            wrappedView = nibName.flatMap {
                return viewFromNib($0)
            }
        }
    }
    
    public private(set) var wrappedView: UIView? {
        didSet {
            oldValue?.removeFromSuperview()
            
            if let view = wrappedView {
                insertSubview(view, atIndex: 0)
                view.translatesAutoresizingMaskIntoConstraints = false

                addConstraint(topAnchor.constraintEqualToAnchor(view.topAnchor))
                addConstraint(leftAnchor.constraintEqualToAnchor(view.leftAnchor))
                addConstraint(rightAnchor.constraintEqualToAnchor(view.rightAnchor))
                addConstraint(bottomAnchor.constraintEqualToAnchor(view.bottomAnchor))
            }
        }
    }
    
    public override func intrinsicContentSize() -> CGSize {
        if let wrappedView = wrappedView {
            return wrappedView.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize)
        } else {
            return CGSize(width: UIViewNoIntrinsicMetric, height: UIViewNoIntrinsicMetric)
        }
    }
    
    private func viewFromNib(name: String) -> UIView? {
        let bundle = NSBundle(forClass: self.dynamicType)
        return bundle.loadNibNamed(name, owner: self, options: nil).first as! UIView?
    }
}