title: Transparent view is black?
body: <p>I'm trying to create a view that is transparent in certain spots to see an image behind.  However, for some reason in the transparent part of the view, I'm seeing black, instead of what's behind the view.  I've trimmed it down to very little code and don't understand why my transparent view shows black instead of red (the color of the view behind).  Here's my code:</p>
  
  <pre><code>class ViewController: UIViewController {
  
      override func viewWillAppear(_ animated: Bool) {
          super.viewWillAppear(animated)
          let redView = UIView(frame: view.frame)
          redView.backgroundColor = UIColor.red
          let transparentView = TransparentView(frame: view.frame)
  
          view.addSubview(redView)
          view.addSubview(transparentView)
      }
  }
  </code></pre>
  
  <p></p>
  
  <pre><code>class TransparentView: UIView {
  
      override func draw(_ rect: CGRect) {
          UIColor.clear.setFill()
          UIRectFill(rect)
  }
  </code></pre>
  
  <p>I would expect the screen to be full red, but instead it shows full black.  Before someone says it's a lot easier to make a clear view, I'm actually trying to do more complex things in drawRect, just dropped down to the most basic thing to try to debug my problem.  What am I missing here?</p>