UIPageViewController not showing anything but black screen - but doesn't throw errors

I am developing an application for iOS using swift. I have already set up one UIPageViewController successfully in my project, so I know how it works. But now I'm trying to set up a second PageViewController, and it just doesn't work - it doesn't throw any errors either, it just goes directly to black screen and doesn't even show any segues

What I have tried so far:

1. Resetting the iOS simulator


2. Reindexing the xcode files


3. Restarting xcode


4. Restarting my machine

None of these things have helped.

My code:

(BTW: This code is almost the exactly same as in my working UIPageViewController, the only difference is in the variables' names)

import UIKit

class SelectDestinationViewController: UIPageViewController, UIPageViewControllerDelegate, UIPageViewControllerDataSource {

var destinationViewControllers : [UIViewController] = []

override func viewDidLoad() {
    super.viewDidLoad()

    println("View did appear")

    // Do any additional setup after loading the view.

    self.delegate = self
    self.dataSource = self

    let firstView = storyboard?.instantiateViewControllerWithIdentifier("firstView") as FirstDestinationViewController
    let secondView = storyboard?.instantiateViewControllerWithIdentifier("secondView") as SecondDestinationViewController

    destinationViewControllers = [firstView, secondView]

    for var index = 0; index < destinationViewControllers.count; ++index {

        println("\(destinationViewControllers[index])")

    }

    let startingViewController = self.viewControllerAtIndex(0)
    let viewControllers: NSArray = [startingViewController]

    self.setViewControllers(viewControllers, direction: UIPageViewControllerNavigationDirection.Forward, animated: true, completion: {(done: Bool) in})
}

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
    println("View will appear!")
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func viewControllerAtIndex(index:NSInteger) -> UIViewController {
    return destinationViewControllers[index]
}

func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {

    var index = find(destinationViewControllers, viewController)!

    if (index == 0) || (index == NSNotFound) {

        return nil

    }

    index--

    if index == destinationViewControllers.count {

        return nil

    }

    return self.viewControllerAtIndex(index)
}

func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {

    var index = find(destinationViewControllers, viewController)!

    if index == NSNotFound {

        return nil

    }

    index++

    if index == destinationViewControllers.count {

        return nil

    }

    return self.viewControllerAtIndex(index)
}

func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int {

    return destinationViewControllers.count

}

func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int {

    return 0

}

}

All the prints are showing up in the console - but nothing else is happening. Does anyone know what the problem might be? Thank you in advance :)