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tvOS, The Focus Engine, and Swift


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As one of the early adopters of Apple TV and tvOS, Gilt Groupe was recently selected to present their “Gilt on TV” app at the Apple Keynote event in September.

This presentation covers Gilt's discoveries during the process of building a tvOS app from scratch in Swift.

It was presented at iOSoho on October 12, 2015 in New York City.

Published in: Technology
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tvOS, The Focus Engine, and Swift

  1. 1. Evan Maloney Distinguished Engineer, Gilt Groupe tvOS, the Focus Engine & Swift Discoveries from building “Gilt on TV”
  2. 2. Demoing “Gilt on TV”
  3. 3. tvOS vs. iOS: Similarities • Most of tvOS is a direct subset of iOS • Familiarity with UIKit will serve you well with tvOS • But, some of the things you may expect won’t be there • No web views • Certain frameworks like MultipeerConnectivity aren’t available • Several UIControls (pickers, steppers, sliders, etc.) • Can use Interface Builder (or not), Swift or Objective-C tvOS tvOS vs. iOS
  4. 4. tvOS vs. iOS: Differences • User interaction is indirect touch • Unlike an iPhone or iPad, the user doesn’t directly manipulate the UI — uses indirect touch like a trackpad • Directionality is reversed from iOS • Relies on the Focus Engine for determining UI state • Only on tvOS — adds extensions to UIViewController, UIView, UITableView, UICollectionView, etc. tvOS tvOS vs. iOS
  5. 5. Focus Engine Philosophy • The Focus Engine is intended to be a black box • You provide inputs that determine the initially focused view • You define where the user can go • Provide some visual indication of focusability • Provide an animation or visual state change upon becoming focused (often handled by the tvOS SDK) • Once your view controller is onscreen and the initial view has become focused, the user should be in control of all state changes • It is considered rude to forcibly change focus on the user tvOS The Focus Engine
  6. 6. What is “Focus”? • A focusable view is one that the user can select with the touch remote • Being focusable implies that the user can perform an action on the view • Focusable views are often “pressable,” like UIButtons • A focused view renders itself to stand out from the others onscreen, usually with one or more of the following attributes: • A larger size • A drop shadow • A highlight color or border tvOS Focus
  7. 7. How does the Focus Engine work? • When the view hierarchy changes, the Focus Engine creates a map of the visible focusable views • If the user navigates in a given direction, the Focus Engine looks for a focusable view in that direction, taking into account each candidate view’s focus frame size & relative position • A candidate for receiving next focus is selected • If the candidate is a table or collection cell, the relevant delegate is given an opportunity to reject focus and another candidate may be selected tvOS The Focus Engine
  8. 8. tvOS The Focus Engine Gilt on TV 1.0 — Women’s Store
  9. 9. tvOS The Focus Engine Focus Frames
  10. 10. How does a view become “Focusable”? • By default, the following views are focusable: • UIControls • Table cells and collection cells • Can be overridden by UICollectionViewDelegate • UIViews that are not otherwise focusable can be made so by overriding canBecomeFocused() • The focused property of a UIView indicates whether the view is currently in focus tvOS Focus
  11. 11. How does a view become “Focused”? • When a view controller is displayed, the focus engine asks for the preferredFocusedView from the relevant views and view controllers to determine which view gets initial focus • From there, the user controls focus using the remote • When the user swipes in a given direction, the Focus Engine selects an appropriate focusable view to get next focus • Developers can use the UIFocusUpdateContext to coordinate animations when views go into and out of focus tvOS Focus
  12. 12. tvOS The Focus Engine Gilt on TV 1.0 — Men’s Store (scrolled)
  13. 13. tvOS The Focus Engine Focus Frames
  14. 14. tvOS The Focus Engine Changing Focus — Unambiguous Move
  15. 15. tvOS The Focus Engine Ambiguous Move — Focus Engine Chooses
  16. 16. tvOS The Focus Engine Sale View
  17. 17. tvOS The Focus Engine Focus Frames
  18. 18. tvOS The Focus Engine Navigating to “Buy Now” — A Near Miss
  19. 19. The Dilemma tvOS Focus Guides How could you solve it? You can’t assume the Focus Engine “sees” focusable views that aren’t in the direct path of the swipe direction tvOS solution Allow a UIView to report to a focus frame that’s larger than the view’s native frame 1. Call parentView.addLayoutGuide(UIFocusGuide) 2. Set the focus guide’s preferredFocusedView 3. Add Auto Layout constraints using the focus guide as you would any UIView
  20. 20. tvOS Focus Guides A focus guide defines a screen rectangle
  21. 21. tvOS Focus Guides Focus is forwarded to the preferredFocusedView
  22. 22. tvOS Focus Guides Allowing a small button to respond to a large frame
  23. 23. Handling scrolling content • You will not be able to present scrolling content in the same way you do in iOS • User can only scroll by navigating to something focusable within a scroll view • The Focus Engine only pays attention to focusable non-hidden views with non-zero alphas that have at least one pixel within the screen bounds • Focusable views and cells that are offscreen won’t be visible to the Focus Engine, so the user can’t navigate to them tvOS The Focus Engine
  24. 24. tvOS Focus Guides Product View
  25. 25. tvOS Focus Guides Focus Frames
  26. 26. Other challenges for tvOS developers • Apparently a lot of people rely on web views for mission-critical screens within their apps — they will be forced to rethink • Restrictions on App Store binaries: • Applications need to be submitted as Bitcode binaries • This includes embedded frameworks, which makes many third-party closed-source frameworks unusable in tvOS • On-device testing — Very few people have development devices, and simulator testing may not reveal all problems tvOS tvOS Development
  27. 27. Fun things about tvOS development • Some of the iOS pain points don’t exist on tvOS • Apple TVs will often be used to stream video — unlike with mobile devices, tvOS developers can assume the presence of low-latency, always-on, high-bandwidth networks • Don’t need to think about screen rotation or size class changes • Only need to develop for a single screen resolution — for now tvOS tvOS Development
  28. 28. A few words about Swift and finally…
  29. 29. Swift — Pain Points • The language is still changing, so major releases of Xcode often require a bit of code rewriting • Usually minimal, and the language is improving as a result • Developer tooling still needs work • Debugger sometimes refuses to cough up variable values • Compiler errors can be vague or misleading • Compiler stability is sometimes an issue • Heavy use of Swift frameworks sometimes doesn’t play nicely with “whole module optimization” • Binaries may not be compatible across compiler versions tvOS Swift
  30. 30. Swift — Advantages • Swift may not be mature, but it is ready for prime-time • Swift absolutely fulfills the promise of more efficient development • An entire class of errors that used to require runtime debugging is now caught by the compiler • Building a stable app takes much less work than Objective-C • I probably spent about ¼ the time debugging as I would have had to do in ObjC • Coding in Swift is an absolute pleasure tvOS Swift
  31. 31. Swift — The Verdict tvOS Swift Do it! You know you’ll “go Swift” eventually… …and the longer you wait, the more you’ll be kicking yourself for not having done it sooner once you finally do!
  32. 32. Evan Maloney Distinguished Engineer, Gilt Groupe A parting gift for you CleanroomLogger — A pure Swift logging engine Simple, lightweight & performant Code goodies!