Continuous scrolling between two UIPageControllers - ios

Question

I am trying to achieve a continuous scrolling in the following situation:
MainViewController (UIViewController) contains an instance of UIPageViewController (transitionStyle: .scroll) which manages two controllers only; ItemsViewController (UIViewController) & ProfileViewController (UIViewController). MainViewController allows scrolling between main and profile controllers horizontally.
Now ProfileViewController contains another instance of UIPageViewController (transitionStyle: .scroll) to scroll horizontally between two UIViewControllers (A & B).
The issue is that when I scroll to ProfileViewController and start scrolling between A & B then I can't scroll (to the right) to go back to ItemsViewController. It seems that the UIPageViewController of ProfileViewController is intercepting the scroll gesture and doesn't pass them to UIPageViewController instance of MainViewController and you will get stuck in ProfileViewController.
Here is some code:
final class MainViewController: UIViewController {
private let pageController: UIPageViewController
let itemsController: ItemsViewController
let profileController: ProfileViewController
private var controllers = [UIViewController]()
private(set) var currentPageIndex = 0
override init(...) {
itemsController = ItemsViewController(...)
controllers.append(itemsController)
profileController = ProfileViewController(...)
controllers.append(profileController)
pageController = UIPageViewController(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
super.init(...)
}
override func viewDidLoad() {
super.viewDidLoad()
configurePageController()
}
func configurePageController() {
pageController.dataSource = self
pageController.delegate = self
pageController.setViewControllers([itemsController], direction: .forward, animated: false)
for view in pageController.view.subviews {
if let scrollView = view as? UIScrollView {
scrollView.delegate = self
break
}
}
}
}
extension MainViewController: UIPageViewControllerDataSource {
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
if let index = controllers.firstIndex(of: viewController) {
if index > 0 {
return controllers[index - 1]
}
else {
return nil
}
}
return nil
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
if let index = controllers.firstIndex(of: viewController) {
if index < controllers.count - 1 {
return controllers[index + 1]
}
else {
return nil
}
}
return nil
}
}
extension MainViewController: UIPageViewControllerDelegate {
func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
guard completed else {
return
}
if let vc = pageController.viewControllers?.first,
let index = controllers.firstIndex(of: vc) {
currentPageIndex = index
}
}
}
// Freeze scrolling on the left and right edges
extension MainViewController: UIScrollViewDelegate {
private func freezScrolling(_ scrollView: UIScrollView) {
if currentPageIndex == 0 && scrollView.contentOffset.x < scrollView.bounds.size.width {
scrollView.contentOffset = CGPoint(x: scrollView.bounds.size.width, y: 0)
}
else if currentPageIndex == controllers.count - 1 && scrollView.contentOffset.x > scrollView.bounds.size.width {
scrollView.contentOffset = CGPoint(x: scrollView.bounds.size.width, y: 0)
}
}
func scrollViewDidScroll(_ scrollView: UIScrollView) {
freezScrolling(scrollView)
}
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
freezScrolling(scrollView)
}
}
final class ProfileViewController: UIViewController {
private let pageController: UIPageViewController
private lazy var controllers: [UIViewController] = [ControllerA, ControllerB]
private var currentPageIndex = 0
override init(...) {
pageController = UIPageViewController(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
super.init(...)
}
override func viewDidLoad() {
super.viewDidLoad()
configurePageController()
}
func configurePageController() {
pageController.dataSource = self
pageController.delegate = self
for view in pageController.view.subviews {
if let scrollView = view as? UIScrollView {
scrollView.delegate = self
break
}
}
}
extension ProfileViewController: UIPageViewControllerDataSource {
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
if let index = controllers.firstIndex(of: viewController), index > 0 {
return controllers[index - 1]
}
return nil
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
if let index = controllers.firstIndex(of: viewController), index < controllers.count - 1 {
return controllers[index + 1]
}
return nil
}
}
extension ProfileViewController: UIPageViewControllerDelegate {
func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
guard completed else {
return
}
if let vc = pageController.viewControllers?.first,
let index = controllers.firstIndex(of: vc) {
currentPageIndex = index
}
}
}
extension ProfileViewController: UIScrollViewDelegate {
func scrollViewDidScroll(_ scrollView: UIScrollView) {
freezScrolling(scrollView)
}
private func freezScrolling(_ scrollView: UIScrollView) {
if currentPageIndex == 0 && scrollView.contentOffset.x < scrollView.bounds.size.width {
scrollView.contentOffset = CGPoint(x: scrollView.bounds.size.width, y: 0)
}
else if currentPageIndex == controllers.count - 1 && scrollView.contentOffset.x > scrollView.bounds.size.width {
scrollView.contentOffset = CGPoint(x: scrollView.bounds.size.width, y: 0)
}
}
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
freezScrolling(scrollView)
}
}