Why does the Xcode "Page-Based Application" project template have a PageController? - ios

Question

I'm learning page controllers and have created a blank app using the Page-Based Application template. By default it creates 12 month pages that you can scroll left to right.
On the storyboard there is a Page View Controller Scene with a Page View Controller. However, in the code, there are commands to create this controller programmatically in the root controller. i.e.
var pageViewController: UIPageViewController?
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
// Configure the page view controller and add it as a child view controller.
self.pageViewController = UIPageViewController(transitionStyle: .pageCurl, navigationOrientation: .horizontal, options: nil)
self.pageViewController!.delegate = self
let startingViewController: DataViewController = self.modelController.viewControllerAtIndex(0, storyboard: self.storyboard!)!
let viewControllers = [startingViewController]
self.pageViewController!.setViewControllers(viewControllers, direction: .forward, animated: false, completion: {done in })
self.pageViewController!.dataSource = self.modelController
self.addChildViewController(self.pageViewController!)
self.view.addSubview(self.pageViewController!.view)
// Set the page view controller's bounds using an inset rect so that self's view is visible around the edges of the pages.
var pageViewRect = self.view.bounds
if UIDevice.current.userInterfaceIdiom == .pad {
pageViewRect = pageViewRect.insetBy(dx: 40.0, dy: 40.0)
}
self.pageViewController!.view.frame = pageViewRect
self.pageViewController!.didMove(toParentViewController: self)
}
In fact, if I delete the Page View Controller from the storyboard, the app works just as before.
I am trying to understand why this would be on the storyboard when it does not appear to be used. Also, are the good reasons to create a Page View Controller programmatically rather than using the storyboard?

Answer 1

Inside storyboard You have a standard UIViewController subclass, not UIPageViewController. Your UIPageViewController is created in code, and then added as a subview to this RootViewController. RootViewController displays UIPageViewController and act as its delegate. I don't think this will work correctly if you delete anything from the storyboard, are you sure about this? There is not instance of UIPageViewController in storyboard.