title: Why does changing the transition style of my UIPageViewController to .scroll make all of the UIViewControllers disappear?
body: <p>I'm trying to change the transition style of my UIPageViewController from the default pageCurl to scroll. I'm trying to do this all programatically. In my code shown below, my two view controllers, <code>teamVC</code> and <code>teamVC2</code> are shown perfectly fine when these two init functions are commented out.</p>
  
  <pre><code>override init(transitionStyle style: UIPageViewController.TransitionStyle, navigationOrientation: UIPageViewController.NavigationOrientation, options: [UIPageViewController.OptionsKey : Any]? = nil) {
      super.init(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
  }
  
  required init?(coder: NSCoder) {
      fatalError("init(coder:) has not been implemented")
  }
  </code></pre>
  
  <p>However, when they're left in and I run the code, nothing appears on the screen. </p>
  
  <pre><code>class PagingViewController: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {
  
  var teamViewControllers: [UIViewController] = []
  
  func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -&gt; UIViewController? {
      let currentIndex = teamViewControllers.firstIndex(of: viewController) ?? 0
      if currentIndex &lt;= 0 {
          return nil
      }
      return teamViewControllers[currentIndex - 1]
  }
  
  func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -&gt; UIViewController? {
      let currentIndex = teamViewControllers.firstIndex(of: viewController) ?? 0
      if currentIndex &gt;= teamViewControllers.count - 1 {
          return nil
      }
      return teamViewControllers[currentIndex + 1]
  }
  func presentationCount(for pageViewController: UIPageViewController) -&gt; Int {
      return teamViewControllers.count
  }
  
  //this function and the required init function below make my view controllers disappear
  override init(transitionStyle style: UIPageViewController.TransitionStyle, navigationOrientation: UIPageViewController.NavigationOrientation, options: [UIPageViewController.OptionsKey : Any]? = nil) {
      super.init(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
  }
  
  required init?(coder: NSCoder) {
      fatalError("init(coder:) has not been implemented")
  }
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      self.delegate = self
      self.dataSource = self
  
      let teamVC = TeamViewController()
      teamVC.teamName = "Atlanta Hawks"
      teamViewControllers.append(teamVC)
  
      let teamVC2 = TeamViewController()
      teamVC2.teamName = "Boston Celtics"
      teamViewControllers.append(teamVC2)
  
      setViewControllers([teamViewControllers[0]], direction: .forward, animated: true, completion: nil)
  }
  }
  </code></pre>