PageViewController

PageViewController.swift

protocol PageControllerIndexable: class {
  var pageIndex: Int { get set }
}

protocol PageViewControllerDatasource: class {
  var startingViewController: PageControllerIndexable? { get }
  var nextViewController: PageControllerIndexable? { get }
  var previousViewController: PageControllerIndexable? { get }
  var currentIndex: Int { get }
}

protocol PageViewControllerDelegate: class {
  func didChangeContentController(_ controller: PageControllerIndexable?)
}

class PageViewController: UIPageViewController {
  
  weak var pagesDatasource: PageViewControllerDatasource?
  weak var pagesDelegate: PageViewControllerDelegate?
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    self.view.backgroundColor = UIColor.clear
    
    dataSource = self
    delegate = self
    
    assert(pagesDatasource != nil, "setup pagesDatasource")
    
    if let vc = pagesDatasource!.startingViewController {
      setViewControllers([vc as! UIViewController],
                         direction: .forward,
                         animated: false,
                         completion: nil)
      vc.pageIndex = pagesDatasource!.currentIndex
      pagesDelegate!.didChangeContentController(vc)
    }
  }
  
  func forward() {
    setup(contentController: pagesDatasource?.nextViewController, forDirection: .forward)
  }
  
  func backward() {
    setup(contentController: pagesDatasource?.previousViewController, forDirection: .reverse)
  }
}

// MARK: UIPageViewControllerDataSource
extension PageViewController: UIPageViewControllerDataSource {
  
  func pageViewController(_ pageViewController: UIPageViewController,
                          viewControllerBefore viewController: UIViewController) -> UIViewController? {
    let previousVC = pagesDatasource!.previousViewController
    previousVC?.pageIndex = (pagesDatasource!.currentIndex - 1)
    return previousVC as? UIViewController
  }
  
  func pageViewController(_ pageViewController: UIPageViewController,
                          viewControllerAfter viewController: UIViewController) -> UIViewController? {
    let nextVC = pagesDatasource!.nextViewController
    nextVC?.pageIndex = (pagesDatasource!.currentIndex + 1)
    return nextVC as? UIViewController
  }
}

// MARK: - UIPageViewControllerDelegate
extension PageViewController: UIPageViewControllerDelegate {
  
  func pageViewController(_ pageViewController: UIPageViewController,
                          didFinishAnimating _: Bool,
                          previousViewControllers _: [UIViewController],
                          transitionCompleted completed: Bool) {
    if !completed {
      return
    }
    pagesDelegate!.didChangeContentController(pageViewController.viewControllers?.first as? PageControllerIndexable)
  }
}

private extension PageViewController {
  
  func setup(contentController viewController: PageControllerIndexable?, forDirection direction: UIPageViewControllerNavigationDirection) {
    if let vc = viewController {
      setViewControllers([vc as! UIViewController], direction: direction, animated: true, completion: nil)
      let side = direction == .reverse ? (-1) : 1
      vc.pageIndex = pagesDatasource!.currentIndex + side
      pagesDelegate!.didChangeContentController(vc)
    }
  }
}