Swifty View Controller Presenters

One major shortcoming of UIKit is that view controllers have too many responsibilities. This talk focuses on one — presenting and dismissing view controllers — and how we can re-examine and redefine the presentation controller API in iOS with a more Swifty API that reduces boilerplate and increases expressivity.

Video:
https://realm.io/news/slug-jesse-squires-swifty-view-controller-presenters/

GitHub project:
https://github.com/jessesquires/PresenterKit

Event:
https://www.meetup.com/swift-language/events/227833264/

Transcript

1. SWIFTY VIEW CONTROLLER PRESENTERS
   JESSE SQUIRES
   JESSESQUIRES.COM • @JESSE_SQUIRES • GITHUB/JESSESQUIRES
   @swiftlybrief
   

   View Slide

2. VIEW CONTROLLERS
   EVERYWHERE
   

   View Slide

3. PRESENTATION CONTROLLERS
   EVERYWHERE
   

   View Slide

4. PRESENTATION
   VS.
   TRANSITION
   

   View Slide

5. What's the difference?
   

   View Slide

6. TRANSITION
   the moving
   (or animating)
   from one view controller
   to another view controller
   

   View Slide

7. PRESENTATION
   the ending visual state
   (or final appearance)
   of a view controller
   after the transition
   

   View Slide

8. BUT...
   

   View Slide

9. TRANSITION VS. PRESENTATION
   Concepts are very interrelated.
   Presentation API hooks into the transitioning API.
   Slightly coupled in this way, but otherwise nicely decoupled.
   

   View Slide

10. PRESENTATION
    UIPresentationController
    iOS 8+
    

    View Slide

11. UIPresentationController
    WAT?
    

    View Slide

12. UIPresentationController
    The APIs are very subtle and usually implicit.
    You often use them without knowing it.
    Typically overlooked.
    Previously, relevant on iPad only.
    

    View Slide

13. UNDERSTANDING
    THE PRESENTATION API
    

    View Slide

14. RESPONSIBILITIES
    ▸ Positioning
    ▸ Content and "Chrome"
    ▸ Adaption
    ▸ Animation
    Intended to be reusable
    

    View Slide

15. 3 PHASES
    1. Presentation (moving onscreen)*
    2. Management (size class changes, device rotation)
    3. Dismissal (moving offscreen)*
    *Transitioning
    

    View Slide

16. EXAMPLES
    

    View Slide

17. View Slide

18. View Slide

19. View Slide

20. UIPresentationController
    Subtle and Implicit
    UIModalPresentationStyle
    // just set an enum!
    self.modalPresentationStyle = .FullScreen
    self.modalPresentationStyle = .Popover
    

    View Slide

21. View Slide

22. PRESENTING
    func presentViewController(_, animated:, completion:)
    func pushViewController(_, animated:)
    func showViewController(_, sender:)
    func showDetailViewController(_, sender:)
    

    View Slide

23. DISMISSING
    func dismissViewControllerAnimated(_, completion:)
    func popViewControllerAnimated(_ animated:) -> UIViewController?
    

    View Slide

24. Special
    PRESENTATIONS
    

    View Slide

25. UIPresentationController
    ▸ UIAlertController
    ▸ UISearchController
    ▸ UIPopoverPresentationController (explicit!)
    Unified, consistent APIs.
    All view controllers with custom presentation controllers.
    

    View Slide

26. UIPopoverPresentationController
    The only custom presentation controller publicly available in UIKit
    // Current UIViewController APIs
    self.presentationController
    self.popoverPresentationController
    

    View Slide

27. PRIVATE API
    // Modal styles: .FullScreen, .FormSheet, .PageSheet, etc.
    _UIFullscreenPresentationController
    // Alerts
    _UIAlertControllerAlertPresentationController
    // ActionSheet on iPhone
    _UIAlertControllerActionSheetCompactPresentationController
    // ActionSheet on iPad (popover)
    _UIAlertControllerActionSheetRegularPresentationController
    

    View Slide

28. API SUMMARY
    ▸ 4 methods to display a view controller
    ▸ Set styles via an enum value
    ▸ Use popoverPresentationController directly
    ▸ Provide a custom Presentation Controller
    

    View Slide

29. The API is easy to misuse.
    

    View Slide

30. #SORRYNOTSORRY
    

    View Slide

31. HOW TO USE
    CUSTOM PRESENTATION
    CONTROLLERS
    

    View Slide

32. CUSTOM PRESENTATION CONTROLLERS
    1. Subclass UIPresentationController
    2. Vend controller via transitioning API
    !
    

    View Slide

33. 1. SUBCLASS: TRANSITIONING AND CHROME
    func presentationTransitionWillBegin()
    func dismissalTransitionWillBegin()
    

    View Slide

34. 1. SUBCLASS: POSITIONING
    func sizeForChildContentContainer(_, withParentContainerSize:) -> CGSize
    func frameOfPresentedViewInContainerView() -> CGRect
    

    View Slide

35. 1. SUBCLASS: ADAPTIVITY
    func adaptivePresentationStyle() -> UIModalPresentationStyle
    func shouldPresentInFullscreen() -> Bool
    func containerViewWillLayoutSubviews()
    

    View Slide

36. 2. VEND CONTROLLER
    UIViewControllerTransitioningDelegate
    Presenting view controller conforms to delegate
    Set this delegate on the Presented view controller
    let vc = MyViewController()
    vc.transitioningDelegate = self
    

    View Slide

37. 2. VEND CONTROLLER
    UIViewControllerTransitioningDelegate
    func presentationControllerForPresentedViewController(_,
    presentingViewController:,
    sourceViewController:) -> UIPresentationController?
    

    View Slide

38. Demo
    

    View Slide

39. BETTER THAN VIEW
    CONTROLLER CONTAINMENT
    

    View Slide

40. Let's build a micro-library
    ▸ Refine this API
    ▸ Make it Swifty
    

    View Slide

41. enum PresentationType {
    case Modal(NavigationStyle, UIModalPresentationStyle, UIModalTransitionStyle)
    case Popover(PopoverConfig)
    case Push
    case Show
    case ShowDetail(NavigationStyle)
    case Custom(UIViewControllerTransitioningDelegate)
    }
    

    View Slide

42. enum NavigationStyle {
    case None
    case WithNavigation
    }
    

    View Slide

43. struct PopoverConfig {
    enum Source {
    case BarButtonItem(UIBarButtonItem)
    case View(UIView)
    }
    let source: Source
    let arrowDirection: UIPopoverArrowDirection
    let delegate: UIPopoverPresentationControllerDelegate?
    }
    

    View Slide

44. extension UIViewController {
    // maps PresentationType to UIKit properties and methods
    func presentViewController(
    controller: UIViewController,
    type: PresentationType,
    animated: Bool = true)
    }
    

    View Slide

45. USAGE
    presentViewController(vc, type: .Push)
    let config = PopoverConfig(source: .View(v))
    presentViewController(vc, type: .Popover(config))
    let type = .Modal(.WithNavigation, .FullScreen, .CoverVertical)
    presentViewController(vc, type: type)
    presentViewController(vc, type: .Custom(self))
    

    View Slide

46. Swifty API
    ▸ More expressive
    ▸ More concise
    ▸ Single "entry point" to API
    ▸ More structured
    (less likely to misuse)
    

    View Slide

47. Additional resources:
    ▸ WWDC 2014 "A Look Inside Presentation Controllers"
    ▸ pspdfkit.com/blog/2015/presentation-controllers/
    ▸ petersteinberger.com/blog/2015/uipresentationcontroller-popover-
    detection/
    

    View Slide

48. Thank you!
    

    View Slide

49. QUESTIONS?
    JESSESQUIRES.COM • @JESSE_SQUIRES • GITHUB/JESSESQUIRES
    

    View Slide