Swift India Conf 2019: Building Apps with Compositional Layout

Speaker: Sowndharya Maheswaran, iOS Developer, Zoho

Twitter: https://twitter.com/_sowndharya/

Bio: An iOS developer working at Zoho. A huge fan of the data handling layer in a product. Loves writing frameworks. A math-aficionado who also spends a considerable amount of time on books on philosophy.

Abstract: Collection Views are the go-to components to build our layouts, however sophisticated they might appear to be. With iOS 13, Apple has provided with a hassle-free, (unpredicted) warning-free solution to arrange our views. In this talk, we’re going to explore all that you need to know about the new ‘Compositional Layout’ to implement interfaces ranging from simple lists to interactive windows.

Transcript

1. Building Apps with Compositional Layouts Sowndharya M iOS Engineer, Zoho Corporation
2. Imagine building this…
3. Nested Collection Views Distinct Layouts Estimated Sizing Paging
4. class PagedCollectionViewLayout: UICollectionViewFlowLayout { static let CollectionViewWidth: CGFloat = screenWidth static let MinimumSpacingBetweenCells: CGFloat = 30 static let DistanceFromEdgeOfScreen: CGFloat = 55 override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint { guard let collectionView = self.collectionView else { return proposedContentOffset } let pageWidth = itemSize.width + PagedCollectionViewLayout.MinimumSpacingBetweenCells let rawPageValue = collectionView.contentOffset.x / pageWidth let currentPage = velocity.x > 0 ? floor(rawPageValue) : ceil(rawPageValue) let nextPage = velocity.x > 0 ? ceil(rawPageValue) : floor(rawPageValue) let pannedLessThanPage = abs(1 + currentPage - rawPageValue) > 0.3 let flicked = abs(velocity.x) > 0.3 var offset = proposedContentOffset if pannedLessThanPage && flicked { offset.x = nextPage * pageWidth } else { offset.x = round(rawPageValue) * pageWidth } return offset } } extension ViewController: UICollectionViewDataSource { func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: TextCell.reuseIdentifier, for: indexPath) as? InnerCollectionCell else { return UICollectionViewCell() } cell.collectionView.delegate = self cell.collectionView.dataSource = self return cell } }
5. Possible in 5 lines of code?
6. What exactly is happening?
7. F E D A B C Flow Layout
8. Leads us to… Nested Scroll Views Self-sizing cells Boilerplate code
9. ! Caution The behavior of the UICollectionViewFlowLayout is not defined because: The item width must be less than the width of the UICollectionView minus the section insets left and right values, minus the content insets left and right values.
10. Compositional Layout
11. Stitching small groups Composing > Sub Classing Compositional Layout
12. //Abstraction Layers size = LayoutSize(width: .fractionalWidth(1.0), height: .absolute(44.0)) item = LayoutItem(layoutSize: size) group = LayoutGroup.horizontal(layoutSize: size, subitems: [item]) section = LayoutSection(group: group) layout = CompositionalLayout(section: section)
13. Layout Section Groups Item
14. Layout Size NSCollectionLayoutSize init(width: LayoutDimension, height: LayoutDimension) Re-defining dimensions
15. Layout Dimension NSCollectionLayoutDimension fractionalWidth(_ fractionalWidth: CGFloat) fractionalHeight(_ fractionalHeight: CGFloat) absolute(_ absoluteDimension: CGFloat) estimated(_ estimatedDimension: CGFloat) Axis Independent Four variants
16. Layout Dimension let widthDimension = NSLayoutDimension.fractionalWidth(0.5) 0.5
17. Layout Dimension let heightDimension = NSLayoutDimension.fractionalHeight(0.3) 0.3
18. Layout Dimension let size = LayoutSize(widthDimension: .fractionalWidth(0.25), heightDimension: .fractionalWidth(0.25)) 0.25 0.25
19. Layout Item NSCollectionLayoutItem init(layoutSize: NSCollectionLayoutSize) var contentInsets: NSDirectionalEdgeInsets Basically a cell…
20. Layout Group NSCollectionLayoutGroup: NSCollectionLayoutItem horizontal(layoutSize: LayoutSize, subitems: [LayoutItem]) vertical(layoutSize: LayoutSize, subitems: [LayoutItem]) custom(layoutSize: LayoutSize, ………) The workhouse Little mini flow layouts
21. Layout Section NSCollectionLayoutSection init(layoutGroup: NSCollectionLayoutGroup) var contentInsets: NSDirectionalEdgeInsets Surprise property!!!
22. The Layout UICollectionViewCompositionalLayout init(section: LayoutSection) init(sectionProvider: @escaping SectionProvider) Includes per section definition
23. Let's Compose
24. Simple Lists
25. 1.0 size = LayoutSize(width: .fractionalWidth(1.0), height: .absolute(44.0)) item = LayoutItem(layoutSize: size) group = LayoutGroup.horizontal(layoutSize: size, subitems: [item]) 1.0
26. Simple Lists
27. Simpler Grids
28. Simpler Grids
29. Can we please address the
 AppStore problem now..?!
30. Estimated Self-Sizing Per axis Dynamic text
31. Distinct Sections
32. layout = CompositionalLayout(section: section) //Or layout = CompositionalLayout { (sectionIndex: Int, layoutEnvironment: LayoutEnvironment) -> LayoutSection? in group = // Based on section section = LayoutSection(group: group) return section } return layout
33. layout = CompositionalLayout(section: section) //Or layout = CompositionalLayout { (sectionIndex: Int, layoutEnvironment: LayoutEnvironment) -> LayoutSection? in group = // Based on section section = LayoutSection(group: group) return section } return layout
34. layout = CompositionalLayout(section: section) //Or layout = CompositionalLayout { (sectionIndex: Int, layoutEnvironment: LayoutEnvironment) -> LayoutSection? in group = // Based on section section = LayoutSection(group: group) return section } return layout
35. Nested Groups
36. Unlimited Possibilities
37. Where is the Nested Collections, Paging in these five lines?
38. There is a 6th Line
39. section.orthogonalScrollingBehavior = .continuous
40. // Orthogonal Scrolling Sections enum Section Orthogonal Scrolling Behavior case none case continuous case continuousGroupLeadingBoundary case paging case groupPaging case groupPagingCentered
41. Case study
42. AppStore
43. Layout
44. Sections
45. Horizontal Group Vertical Group
46. Horizontal Group Vertical Group Item Width - 1.0 Item Count - 3
47. Pinterest
48. Layout
49. Horizontal
 Group Group Width - 0.5
50. Vertical
 Groups Item Height - Absolute
51. Credits https://developer.apple.com/videos/play/wwdc2019/215 https://github.com/jVirus/compositional-layouts-kit https://gist.github.com/breeno/f16330c5ef06075b0fc476c65d9b00d8