title: Get height / width of uiview set using contraints
body: <p>How can I retrieve the calculated height/width of a <code>UIView</code> is the height and/or width was let using a <code>NSConstraint</code> ?</p>
  
  <p>To explain differently:
  I would like to retrieve the <code>CGFloat</code> value of a <code>UIView's</code> "width" or "height" after the element has been laid out using autolayout and constraints. </p>