title: Swift: How to resize UIView and keep contents centered?
body: <p>I have a UIView ("myUIView") in my ViewController ("mainView") that has a UILabel ("myUILabel") inside, centered vertically with autolayout constraints. I'm animating this UIView to change its height. </p>
  
  <p>Originally, I thought auto layout would keep track of the animation/change and keep the UILabel centered, but instead the UILabel acts as though it is constrained to the top of the UIView.</p>
  
  <p>The UILabel isn't in the animation code itself. Code for reference:</p>
  
  <pre><code>UIView.animateWithDuration(currentAnimationTime, delay: 0.0, options: .CurveEaseOut, animations: { 
  self.myUIView.frame = CGRectMake(0, self.mainView.frame.height * 0.2, self.mainView.frame.width, self.mainView.frame.height * 0.6 )
  }, completion: nil)
  </code></pre>
  
  <p>How can I increase the UIView's height and keep my UILabel entered vertically? Will I need to add something that directly affects the UILabel itself, or am I going about the resize itself (CGRectMake) all wrong?</p>