title: @IBDesignable class with .xib-File not rendering in Interface Builder
body: <p>I have a <code>CustomClass.swift</code> and a <code>CustomClass.xib</code>. I want XCode's Interface Builder to render views of class <code>CustomClass</code> using the provided .xib-File. Just like it does when I run the app.</p>
  
  <p>I am using XCode <strong>8.3.2 (8E2002)</strong></p>
  
  <h2>CustomClass.swift</h2>
  
  <pre><code>import UIKit
  
  
  @IBDesignable class forceInterface: UIView {
  
      override init(frame: CGRect) {
          super.init(frame: frame)
      }
  
      required init?(coder aDecoder: NSCoder) {
          super.init(coder: aDecoder)
          Bundle.main.loadNibNamed("forceInterface", owner: self, options: nil)
          self.addSubview(view)
          view.frame = self.bounds
  
      }
  
  
  
      @IBOutlet var view: UIView!
      @IBOutlet weak var label: UILabel!
      @IBOutlet weak var progressView: UIProgressView!
  
      override func prepareForInterfaceBuilder() {
          super.prepareForInterfaceBuilder()
  
      }
  }
  </code></pre>
  
  <h2>CustomClass.xib</h2>
  
  <p>File owner is set to <code>CustomClass</code>. It contains a <code>UIView</code> that contains a <code>UISwitch</code> and a <code>UILabel</code>.
  <a href="https://i.stack.imgur.com/9M5Nj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9M5Nj.png" alt="CustomClass.xib"></a></p>
  
  <p>The problem is that, eventhough I have <code>@IBDesignable</code> in my <code>CustomClass.swift</code>, it isn't rendering in the InterfaceBuilder. I am placing a <code>UIView</code> there and setting its class to <code>CustomClass</code>:
  <a href="https://i.stack.imgur.com/n3wPd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/n3wPd.png" alt="enter image description here"></a></p>
  
  <p>As you can see, it even says <em>Designables: Up to date</em> in the inspector. But I am not seeing anything.</p>
  
  <p><strong>When running the app everything works as expected!</strong></p>