IOS UIPageViewController second view not loading - ios

Question

I have a problem with my PageViewController. It works as expected when I switch views by taping on the page indicators, but when I swipe every second view is blank (black).The preview while swiping is displayed properly, but when I complete the swipe the view disappears.
import UIKit
class ScheduleViewController: UIViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {
#IBAction func editButton(sender: AnyObject) {
(self.pageViewController.view as! UITableView).setEditing(true, animated: true)
print((self.pageViewController.view as! UITableView).editing)
}
#IBOutlet weak var navBar: UINavigationItem!
var pageViewController: UIPageViewController!
var index = 0
var viewControllers: [ContentViewController] = []
override func viewDidLoad()
{
self.navigationController!.navigationBar.translucent = false
self.tabBarController!.tabBar.translucent = false
self.pageViewController = self.storyboard?.instantiateViewControllerWithIdentifier("ScheduleViewControllerPage") as! UIPageViewController
self.pageViewController.dataSource = self
self.pageViewController.delegate = self
for a in [0,1,2,3,4]{
var vc: ContentViewController = self.storyboard?.instantiateViewControllerWithIdentifier("ContentViewController") as! ContentViewController
vc.pageIndex = a
vc.tableView.reloadData()
self.viewControllers.append(vc)
}
print(viewControllers)
self.pageViewController.setViewControllers([self.viewControllers[0]] as [UIViewController], direction: .Forward, animated: false, completion: nil)
self.pageViewController.view.frame = CGRectMake(0, 0, self.view.frame.width, self.view.frame.size.height)
self.addChildViewController(self.pageViewController)
self.view.addSubview(self.pageViewController.view)
self.pageViewController.didMoveToParentViewController(self)
super.viewDidLoad()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController?
{
index--
if index <= -1 {
index = 4
}
return self.viewControllers[index] as UIViewController
}
func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
index++
if index >= 5 {
index = 0
}
return self.viewControllers[index] as UIViewController
}
func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int
{
return 5
}
func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int
{
return index
}
}