UIPageViewController with bug - ios

Question

My UIPageViewController crashes when the DataSource methods ViewControllerAfter and ViewControllerBefore returns nil (which should only mean that there's no more pages to show). It crashes with the message:
'The number of view controllers provided (0) doesn't match the number
required (1) for the requested transition'
Thanks! Please help!
My initialization code:
self.pageController = UIPageViewController(transitionStyle: .pageCurl, navigationOrientation: .horizontal, options: nil)
self.pageController?.dataSource = self
// self.pageController?.delegate = self
self.pageController?.setViewControllers([self.controller.pages.first!], direction: .forward, animated: true, completion: nil)
self.updateControls()
self.addChildViewController(self.pageController!)
self.view.addSubview((self.pageController?.view)!)
self.pageController?.didMove(toParentViewController: self)
And below my DataSource code:
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
previousIndex = self.controller.pages[self.currentPage].pageIndex!
if previousIndex <= 0 {
print("entrou no nil do before")
return nil
}
self.previousIndex -= 1
self.currentPage = self.previousIndex
return self.controller.pages[previousIndex]
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
nextIndex = self.controller.pages[self.currentPage].pageIndex!
nextIndex += 1
if (nextIndex == self.controller.pages.count) {
print("entrou no nil do after")
return nil
}
self.currentPage = nextIndex
return self.controller.pages[nextIndex]
}

Answer 1

Both the methods will return nil due to its behaviour. You need to handle it at your own.
This flexibility is given to put the pages in pageviewcontroller in cycle or end it on number of pages.
You need to use such code:
// MARK: - PageViewControllerDataSource
//Array of viewcontroller (pages) identifiers.
var pageTitles = [String]
func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {
let identifier = viewController.restorationIdentifier
var index = self.pageTitles.indexOf(identifier!)!
print("index back = \(index)")
if index == 0 {
currentPageCount = -1
nextPageCount = index
}
if index == 0 || index == NSNotFound {
return nil
}
index -= 1
currentPageCount = index-1
nextPageCount = index
return self.viewControllerAtIndex(index)
}
func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
let identifier = viewController.restorationIdentifier
var index = self.pageTitles.indexOf(identifier!)!
if index == NSNotFound {
return nil;
}
index += 1
if index == self.pageTitles.count {
return nil;
}
return self.viewControllerAtIndex(index)
}