UIStoryboardSegue: top view is not sliding down - ios

Question

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.
Currently there is no animation and it just flashes to the secondVCView.
Many Thanks
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: { () -> Void in
firstVCView.frame = CGRectOffset(firstVCView.frame, 0.0, screenHeight)
//secondVCView.frame = CGRectOffset(secondVCView.frame, -screenWidth, 0.0)
}) { (Finished) -> Void in
self.sourceViewController.presentViewController(self.destinationViewController as! UIViewController,
animated: false,
completion: nil)
}
}
}

Answer 1

As far as I know you need to call layoutIfNeed inside animateWithduration block in order to get a smooth animation.
Greetings

Answer 2

Im not sure if this is the correct way to do this but i managed to get it working by inserting both views.
L
--
import UIKit
class TopToBottomSegue: UIStoryboardSegue {
override func perform() {
// Assign the source and destination views to local variables.
let firstVCView = self.sourceViewController.view as UIView!
let secondVCView = self.destinationViewController.view as UIView!
// Get the screen width, height and status bar height.
let screenWidth = UIScreen.mainScreen().bounds.size.width
let screenHeight = UIScreen.mainScreen().bounds.size.height
let statusBarHeight = self.statusBarHeight()
// Specify the initial position of both views.
secondVCView.frame = CGRectMake(0.0, 0.0, screenWidth, screenHeight)
firstVCView.frame = CGRectMake(0.0, statusBarHeight, 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(firstVCView, aboveSubview: secondVCView)
window?.insertSubview(secondVCView, belowSubview: firstVCView)
// Animate the transition.
UIView.animateWithDuration(0.3, animations: { () -> Void in
firstVCView.frame = CGRectOffset(firstVCView.frame, 0.0, screenHeight)
}) { (Finished) -> Void in
self.sourceViewController.presentViewController(self.destinationViewController as UIViewController,
animated: false,
completion: nil)
}
}
func statusBarHeight() -> CGFloat {
let statusBarSize = UIApplication.sharedApplication().statusBarFrame.size
return Swift.min(statusBarSize.width, statusBarSize.height)
}
}