I have been struggling with this issue for the last few days and after all this juggling I have figured out that all I need is the current Index from the datasource method to up
for swift:
func pageViewController(pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool){
let pageContentViewController = pageViewController.viewControllers![0] as! ViewController
let index = pageContentViewController.pageIndex
}