title: UITraitCollection Clarification
body: <p>I'm trying to figure out how to use <code>UITraitCollection</code> programatically, but I find it difficult to make sense of it. I'm developing for an iPad retina, in iOS 8.</p>
  
  <p><code>println(self.traitCollection)</code> returns the following output:</p>
  
  <pre><code> &lt;UITraitCollection: 0x10df4c7f0; _UITraitNameUserInterfaceIdiom = Pad,
   _UITraitNameDisplayScale = 2.000000, _UITraitNameHorizontalSizeClass = Regular, 
   _UITraitNameVerticalSizeClass = Regular, _UITraitNameTouchLevel = 0, 
   _UITraitNameInteractionModel = 1&gt;
  </code></pre>
  
  <p>Which is pretty straight forward.
  But when I then rotate the screen, I get the exact same output. I.e., same vertical size class, and same horizontal size class.</p>
  
  <p>So my question is, do I need to specify the size class I want for each device orientation (as far as I can see, the size classes are read-only properties!) or am I missing something obvious?
  In the example given in the 'What's new in Cocoa-Touch' talk on the WWDC 2014 video site, he uses the iPhone as an example, which has different vertical / horizontal size classes for each device orientation.</p>
  
  <p>How would you go about this?</p>