Parchment Documentation

To provide data to a PagingViewController, implement the PagingViewControllerDataSource protocol. You must define the total number of view controllers, provide a UIViewController for a specific index, and provide a PagingItem (such as PagingIndexItem) for that index.

Note that viewControllerAt is only called for the currently selected item and its immediate siblings to optimize memory allocation.

class ViewController: UIViewController, PagingViewControllerDataSource {
    let cities = ["Oslo", "Stockholm", "Tokyo", "Barcelona", "Vancouver", "Berlin"]

    func numberOfViewControllers(in pagingViewController: PagingViewController) -> Int {
        return cities.count
    }

    func pagingViewController(_: PagingViewController, viewControllerAt index: Int) -> UIViewController {
        return CityViewController(city: cities[index])
    }

    func pagingViewController(_: PagingViewController, pagingItemAt index: Int) -> PagingItem {
        return PagingIndexItem(index: index, title: cities[index])
    }
}

// Setup
let pagingViewController = PagingViewController()
pagingViewController.dataSource = self

Use the PagingViewControllerInfiniteDataSource protocol when the number of view controllers is unknown or potentially infinite (e.g., a calendar or server-side paginated data).

To implement this, you must:

1. Define a custom type that conforms to PagingItem, Hashable, and Comparable to represent your data.
2. Conform to PagingViewControllerInfiniteDataSource by implementing three methods:
   • pagingViewController(_:itemAfter:): Returns the next PagingItem after the current one.
   • pagingViewController(_:itemBefore:): Returns the previous PagingItem before the current one.
   • pagingViewController(_:viewControllerFor:): Returns the UIViewController associated with the given PagingItem.
3. Assign the data source to the infiniteDataSource property of your PagingViewController instance.
4. Call select(pagingItem:) to set the starting item.

// 1. Define your custom PagingItem
struct CalendarItem: PagingItem, Hashable, Comparable {
    let date: Date
  
    static func < (lhs: CalendarItem, rhs: CalendarItem) -> Bool {
        return lhs.date < rhs.date
    }
}

// 2. Conform to the infinite data source protocol
extension ViewController: PagingViewControllerInfiniteDataSource {
  func pagingViewController(_: PagingViewController, itemAfter pagingItem: PagingItem) -> PagingItem? {
    let calendarItem = pagingItem as! CalendarItem
    return CalendarItem(date: calendarItem.date.addingTimeInterval(86400))
  }
  
  func pagingViewController(_: PagingViewController, itemBefore pagingItem: PagingItem) -> PagingItem? {
    let calendarItem = pagingItem as! CalendarItem
    return CalendarItem(date: calendarItem.date.addingTimeInterval(-86400))
  }
  
  func pagingViewController(_: PagingViewController, viewControllerFor pagingItem: PagingItem) -> UIViewController {
    let calendarItem = pagingItem as! CalendarItem
    return CalendarViewController(date: calendarItem.date)
  }
}

// 3. Setup the PagingViewController
let pagingViewController = PagingViewController()
pagingViewController.infiniteDataSource = self
pagingViewController.select(pagingItem: CalendarItem(date: Date()))

To use Parchment, initialize a PagingViewController with an array of UIViewController instances that you want to display. Parchment will automatically generate menu items for each view controller based on their title property.

After initialization, you must add the pagingViewController as a child view controller and set up its layout constraints to fill the parent view.

import Parchment

class ViewController: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()
    let firstViewController = UIViewController()
    let secondViewController = UIViewController()

    let pagingViewController = PagingViewController(viewControllers: [
      firstViewController,
      secondViewController
    ])

    addChild(pagingViewController)
    view.addSubview(pagingViewController.view)
    pagingViewController.didMove(toParent: self)
    pagingViewController.view.translatesAutoresizingMaskIntoConstraints = false

    NSLayoutConstraint.activate([
      pagingViewController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
      pagingViewController.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
      pagingViewController.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
      pagingViewController.view.topAnchor.constraint(equalTo: view.topAnchor)
    ])
  }
}