Got nil for delegate at ViewController included in UIPageViewController - ios

Question

I have a UIPageViewController and several ViewControllers in it. And I want to perform a function in UIPageViewController from a ViewController using delegate protocol. But get nil in the delegate. Can anybody determine what I'm doing wrong?
PageViewController.swift
import UIKit
class PageViewController: UIPageViewController, UIPageViewControllerDelegate, UIPageViewControllerDataSource, Storyboarded {
weak var coordinator: MainCoordinator?
lazy var orderedViewControllers: [UIViewController] = {
return [self.newInstanceVC(viewController: "FirstLoadViewController"), self.newInstanceVC(viewController: "FirstLoad2ViewController")]
}()
var pageControl = UIPageControl()
override func viewDidLoad() {
super.viewDidLoad()
let storyboardVC = newInstanceVC(viewController: "FirstLoad2ViewController") as? FirstLoad2ViewController
storyboardVC?.delegate = self
self.dataSource = self
if let firstViewController = orderedViewControllers.first {
setViewControllers([firstViewController], direction: .forward, animated: true, completion: nil)
}
self.delegate = self
configurePageControl()
}
func configurePageControl() {
pageControl = UIPageControl(frame: CGRect(x: 0, y: UIScreen.main.bounds.maxY - 50, width: UIScreen.main.bounds.width, height: 50))
pageControl.numberOfPages = orderedViewControllers.count
pageControl.currentPage = 0
//pageControl.tintColor = .red
pageControl.pageIndicatorTintColor = .systemGray5
pageControl.currentPageIndicatorTintColor = .systemGray
self.view.addSubview(pageControl)
}
//return view controller by string identifier
func newInstanceVC(viewController: String) -> UIViewController {
return UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: viewController)
}
//MARK: - Setup page controllers
// view controller that appears on swiping to the -> (left)
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
guard let viewControllerIndex = orderedViewControllers.firstIndex(of: viewController) else {
return nil
}
let previousIndex = viewControllerIndex - 1
guard previousIndex >= 0 else {
//return view controller from the end if it is last index from the left side (infinit scroll)
//return orderedViewControllers.last
return nil
}
guard orderedViewControllers.count >= previousIndex else {
return nil
}
return orderedViewControllers[previousIndex]
}
// view controller that appears on swiping to the <- (right)
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
guard let viewControllerIndex = orderedViewControllers.firstIndex(of: viewController) else {
return nil
}
let nextIndex = viewControllerIndex + 1
guard orderedViewControllers.count != nextIndex else {
//return view controller from the begining if it is last index from the right side (infinit scroll)
//return orderedViewControllers.first
return nil
}
guard orderedViewControllers.count > nextIndex else {
return nil
}
return orderedViewControllers[nextIndex]
}
func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
//switch the bullet of the page
let pageContentVievController = pageViewController.viewControllers![0]
self.pageControl.currentPage = orderedViewControllers.firstIndex(of: pageContentVievController)!
}
}
extension PageViewController: PageViewDelegate {
func handleButtonTap() {
coordinator?.goToMainFromPresentation()
}
}
OneOfTheViewControllers.swift
import UIKit
protocol PageViewDelegate: class {
func handleButtonTap()
}
class FirstLoad2ViewController: UIViewController, Storyboarded {
weak var coordinator: MainCoordinator?
weak var child: ChildCoordinator?
weak var delegate: PageViewDelegate?
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func toMainScreenTap(_ sender: Any) {
delegate!.handleButtonTap() //got nil for delegate here
}
}

Answer 1

The problem is simple, it's hiding in your viewDidLoad() method inside PageViewController
...
override func viewDidLoad() {
super.viewDidLoad()
let storyboardVC = newInstanceVC(viewController: "FirstLoad2ViewController") as? FirstLoad2ViewController
storyboardVC?.delegate = self
...
}
/// (storyboardVC) --- will be destroyed when out of viewDidLoad() scope.
So, why you getting your storyboardVC?.delegate = self nil? Because you created storyboardVC property inside viewDidLoad() method and nothing is keeping reference to it. So, at the end viewDidLoad() method it just deinitialize as well as it's PageViewDelegate delegate