title: Swift Autolayout callback function once layout is laid out
body: <p>How do I know when the auto-layouts are laid out?</p>
  
  <p>Is there a callback function?</p>
  
  <p>I am using SnapKit, and I would like to setup few things when my views are laid out. </p>
  
  <p>I have something like below, </p>
  
  <pre><code>vehicleGroup.snp_makeConstraints { (make) -&gt; Void in
      make.width.equalTo(self.headerView).offset(-20)
      make.centerX.equalTo(self)
      make.top.bottom.equalTo(self.headerView)
  }
  </code></pre>
  
  <p>Once the above view is laid out I want to use the width and height of the view like below,</p>
  
  <pre><code>vehicleGroup.contentSize = CGSize(width: vehicleGroup.frame.width, height: vehicleGroup.frame.size.height)
  </code></pre>