title: Force UIViewController to layout correctly without bringing it onto the screen
body: <p>I am having some difficulty with the following problem. I have laid out a UIViewController in Storyboard with the correct constraints. It has all the same views as the UIViewController on the screen at the present. I am using this new UIViewController for some resizing. Therefore, I would like to initialize this UIViewController, layout all the subviews, according to the constraints I have given it, and then use the UIView's frames for the primary UIViewController. Since I never need this secondary UIViewController, it is never displayed. </p>
  
  <p>I instantiate the secondary UIViewController as follows:</p>
  
  <pre><code>secondaryVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewControllerWithIdentifier("secondaryVCId") as? secondaryVC
  </code></pre>
  
  <p>This works fine, but getting the positions of the subviews, the most important thing, does not. Even though the view is sized correctly, (i.e. when <code>secondaryVC.view.size</code> is printed, it is the same as <code>primaryVC.view.size</code>) but the subviews still think that the view is 600 x 600. I have tried many things to force the subviews to layout again, but none seem to work, other than adding the view as a subview, (i.e. <code>primaryVC.view.addSubview(secondaryVC.view)</code>) which I would prefer not to do, (because I would then have to remove it again.)</p>