title: UIStoryboardSegue: top view is not sliding down
body: <p>I have the following swift code and what i am trying to achieve is a segue that slides off the top. I want the secondVCView to be below the firstVCView and for the firstVCView to slide off displaying the secondVCView.</p>
  
  <p>Currently there is no animation and it just flashes to the secondVCView.</p>
  
  <p>Many Thanks</p>
  
  <pre><code>import UIKit
  
  class TopToBottomSegue: UIStoryboardSegue {
  
  override func perform() {
  
      // Assign the source and destination views to local variables.
      var firstVCView = self.sourceViewController.view as UIView!
      var secondVCView = self.destinationViewController.view as UIView!
  
      // Get the screen width and height.
      let screenWidth = UIScreen.mainScreen().bounds.size.width
      let screenHeight = UIScreen.mainScreen().bounds.size.height
  
      // Specify the initial position of the destination view.
      secondVCView.frame = CGRectMake(0, 0, screenWidth, screenHeight)
  
      // Access the app's key window and insert the destination view below the current (source) one.
      let window = UIApplication.sharedApplication().keyWindow
      window?.insertSubview(secondVCView, belowSubview: firstVCView)
  
      // Animate the transition.
      UIView.animateWithDuration(0.4, animations: { () -&gt; Void in
  
          firstVCView.frame = CGRectOffset(firstVCView.frame, 0.0, screenHeight)
          //secondVCView.frame = CGRectOffset(secondVCView.frame, -screenWidth, 0.0)
  
          }) { (Finished) -&gt; Void in
              self.sourceViewController.presentViewController(self.destinationViewController as! UIViewController,
                  animated: false,
                  completion: nil)
      }
  
    }
  }
  </code></pre>