Custom Segue: Going from Top to Bottom - ios

Question

I am attempting to segue by having the source view controller go from the top to bottom. I can get the transition to go from top to bottom, but as the transition is happening, there is a black rectangle that goes from top to bottom. And once that's finished, the destination view controller pops up. Anybody know how to solve this problem? I am using this tutorial: http://www.appcoda.com/custom-segue-animations/ and changing bits and piece of it to do what I want it to do.
import UIKit
class FirstCustomSegue: UIStoryboardSegue {
override func perform() {
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, 0, screenWidth, screenHeight)
// Access the app's key window and insert the destination view above the current (source) one.
let window = UIApplication.sharedApplication().keyWindow
window?.insertSubview(secondVCView, aboveSubview: firstVCView)
// Animate the transition.
UIView.animateWithDuration(2, animations: { () -> Void in
firstVCView.frame = CGRectOffset(firstVCView.frame, 0.0, screenHeight)
secondVCView.frame = CGRectOffset(secondVCView.frame, 0.0, screenHeight)
}) { (Finished) -> Void in
self.sourceViewController.presentViewController(self.destinationViewController as! UIViewController,
animated: false,
completion: nil)
}
}
}

Answer 1

Update your code like this, Is it working correctly now ?
secondVCView.frame = CGRectMake(0.0, -screenHeight, screenWidth, screenHeight)

Answer 2

For those who are looking for the full solution in Swift 4:
override func perform() {
let firstVCView = self.source.view
let secondVCView = self.destination.view
// Get the screen width and height.
let screenWidth = UIScreen.main.bounds.size.width
let screenHeight = UIScreen.main.bounds.size.height
// Specify the initial position of the destination view.
secondVCView!.frame = CGRect(x: 0, y: -screenHeight, width: screenWidth, height: screenHeight)
// Access the app's key window and insert the destination view above the current (source) one.
let window = UIApplication.shared.keyWindow
window?.insertSubview(secondVCView!, aboveSubview: firstVCView!)
// Animate the transition.
UIView.animate(withDuration: 1, animations: { () -> Void in
firstVCView?.frame = (firstVCView?.frame.offsetBy(dx: 0, dy: screenHeight))!
secondVCView?.frame = (secondVCView?.frame.offsetBy(dx: 0, dy: screenHeight))!
}) { (finished) -> Void in
self.source.present(self.destination, animated: false, completion: nil)
}
}