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Backporting Collection View Compositional Layouts Kishikawa Katsumi

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Agenda • What is Collection View Compositional Layouts? • What problem does it solve? • Anatomy: Compositional Layouts • Backporting Collection View Compositional Layouts

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What is Collection View Compositional Layouts?

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What is Collection View Compositional Layouts? • New API introduced by iOS 13 • Extremely easy to build custom complex collection view layouts • Powerful features to beat complex layouts for modern apps

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https://developer.apple.com/videos/play/wwdc2019/215/ WWDC 2019

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https://developer.apple.com/videos/play/wwdc2019/215/ WWDC 2019

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Example: App Store.app

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Modern App UI is Complicated! • Various rich contents
 must be displayed • Various sizes of content are
 on a scroll view • Nested scrolling

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How to make it? • Collection View or
 Stack View with Scroll View? • Collection View on Collection View • Collection View Custom Layouts

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Problem: Building Custom Collection View Layouts

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How to Build Custom Collection View Layouts • Subclass UICollectionViewLayout • Override methods as needed.

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The problem Why difficult to build custom collection view layouts

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Why Difficult to Build Custom Collection View Layouts? • Implement everything yourself • I don't know where to start • Error prone • Too flexible, overkill

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UICollectionViewLayout class UICollectionViewLayout { class var layoutAttributesClass: AnyClass class var invalidationContextClass: AnyClass func prepare() func layoutAttributesForElements(in rect: CGRect) func layoutAttributesForItem(at indexPath: IndexPath) func layoutAttributesForSupplementaryView(ofKind: String, at: IndexPath) func layoutAttributesForDecorationView(ofKind: String, at: IndexPath) func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) func invalidationContext(forBoundsChange newBounds: CGRect) func shouldInvalidateLayout(forPreferredLayoutAttributes:, withOriginalAttributes:) func invalidationContext(forPreferredLayoutAttributes:, withOriginalAttributes:) func targetContentOffset(forProposedContentOffset: CGPoint, withScrollingVelocity: CGPoint) func targetContentOffset(forProposedContentOffset: CGPoint) var collectionViewContentSize: CGSize ...

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Easy Simple Complex Collection View on Collection View Custom Layouts Hard Flow Layout Layout Layout

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Easy Simple Complex Collection View on Collection View Custom Layouts Hard Flow Layout Implementation Layout Layout

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Easy Simple Complex Collection View on Collection View Custom Layouts Hard Flow Layout Compositional Layouts Implementation Layout Layout

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Anatomy: Compositional Layouts

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App Store.app

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Layout, Section, Group, Item Anatomy: Compositional Layouts

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Layout, Section, Group, Item Anatomy: Compositional Layouts

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Layout, Section, Group, Item Anatomy: Compositional Layouts

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Layout, Section, Group, Item Anatomy: Compositional Layouts

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Layout, Section, Group, Item Anatomy: Compositional Layouts

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Layout, Section, Group, Item Layout

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Layout, Section, Group, Item Layout Section

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Layout, Section, Group, Item Section Layout

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Layout, Section, Group, Item Section Layout

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Layout, Section, Group, Item Layout Section Group

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Layout, Section, Group, Item Layout Section Group

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Layout, Section, Group, Item Layout Section Group

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Layout, Section, Group, Item Layout Section Group

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Layout, Section, Group, Item Layout Section Group

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Layout, Section, Group, Item Layout Section Group

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Layout, Section, Group, Item Layout Section Group Item

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Layout, Section, Group, Item Layout Section Group Item

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Layout, Section, Group, Item Layout Section Group Item

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Layout, Section, Group, Item Layout Section Group Item

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Layout, Section, Group, Item Layout Section Group Item

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Layout, Section, Group, Item Layout Section Group Item

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Section

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Group

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Group Item

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let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) let item = NSCollectionLayoutItem(layoutSize: itemSize) let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .absolute(50)) let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item]) let section = NSCollectionLayoutSection(group: group)

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let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) let item = NSCollectionLayoutItem(layoutSize: itemSize) let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .absolute(50)) let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item]) let section = NSCollectionLayoutSection(group: group)

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let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) let item = NSCollectionLayoutItem(layoutSize: itemSize) let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .absolute(50)) let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item]) let section = NSCollectionLayoutSection(group: group)

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let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) let item = NSCollectionLayoutItem(layoutSize: itemSize) let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .absolute(50)) let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item]) let section = NSCollectionLayoutSection(group: group)

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let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) let item = NSCollectionLayoutItem(layoutSize: itemSize) let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .absolute(50)) let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item]) let section = NSCollectionLayoutSection(group: group)

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let itemSize = ...Size(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) 100% 100%

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let itemSize = ...Size(widthDimension: .fractionalWidth(0.5), heightDimension: .fractionalHeight(1)) 50% 100% 50% 100%

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let groupSize = ...Size(widthDimension: .fractionalWidth(1), heightDimension: .absolute(50)) 100% 50pt

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let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) let item = NSCollectionLayoutItem(layoutSize: itemSize) let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .absolute(50)) let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item]) let section = NSCollectionLayoutSection(group: group)

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let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) let item = NSCollectionLayoutItem(layoutSize: itemSize) let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.92), heightDimension: .fractionalHeight(0.4)) let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item]) let section = NSCollectionLayoutSection(group: group)

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let groupSize = ...Size(widthDimension: .fractionalWidth(0.92), heightDimension: .fractionalHeight(0.4)) 92% 40%

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let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1)) let item = NSCollectionLayoutItem(layoutSize: itemSize) let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.92), heightDimension: .fractionalHeight(0.3)) let group = NSCollectionLayoutGroup.vertical(layoutSize: groupSize, subitem: item, count: 3) let section = NSCollectionLayoutSection(group: group)

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let group = NSCollectionLayoutGroup.vertical(layoutSize: groupSize, subitem: item, count: 3)

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let layout = UICollectionViewCompositionalLayout { (sectionIndex, environment) -> NSCollectionLayoutSection? in switch sectionIndex { case 0: ... return section case 1: ... return section ... } } Compose Them into Layout

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... let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.92), heightDimension: .fractionalHeight(0.4)) let group = NSCollectionLayoutGroup.vertical(layoutSize: groupSize, subitems: [itemGroup]) let section = NSCollectionLayoutSection(group: group) section.orthogonalScrollingBehavior = .groupPagingCentered

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Orthogonal Scrolling Behavior ... let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.92), heightDimension: .fractionalHeight(0.4)) let group = NSCollectionLayoutGroup.vertical(layoutSize: groupSize, subitems: [itemGroup]) let section = NSCollectionLayoutSection(group: group) section.orthogonalScrollingBehavior = .groupPagingCentered

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https://github.com/kishikawakatsumi/AppStore-Clone-CollectionViewCompositionalLayouts

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Only iOS 13?

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https://github.com/kishikawakatsumi/IBPCollectionViewCompositionalLayout

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IBPCollectionViewCompositionalLayout

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Under development ✅ Spacing ✅ Nested Groups ✅ Supplemental Views (e.g. Section Header/Footers) ✅ Pinned Section Header/Footers ✅ Orthogonal Scrolling Behavior ✅ Estimated Size (Autosizing) ✅ Custom Group Item (Absolute Positions) ✅ Drop-in replacement ❌ RTL Support

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Drop-in Replacement - (instancetype)initWithSection:(IBPNSCollectionLayoutSection *)section { if (@available(iOS 13, *)) { return [[NSClassFromString(@"UICollectionViewCompositionalLayout") alloc] initWithSection:section]; } else { IBPUICollectionViewCompositionalLayoutConfiguration *configuration = [IBPUICollectionViewCompositionalLayoutConfiguration defaultConfiguration]; return [self initWithSection:section configuration:configuration]; } }

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UICollectionViewLayout class UICollectionViewLayout { ... func prepare() func layoutAttributesForElements(in rect: CGRect) -> [UICollecti func layoutAttributesForItem(at indexPath: IndexPath) -> UIColle func layoutAttributesForSupplementaryView(ofKind elementKind: St func layoutAttributesForDecorationView(ofKind elementKind: Strin func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) - ... var collectionViewContentSize: CGSize { get } ...

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UICollectionViewLayout class UICollectionViewLayout { ... func prepare() func layoutAttributesForElements(in rect: CGRect) -> [UICollecti func layoutAttributesForItem(at indexPath: IndexPath) -> UIColle func layoutAttributesForSupplementaryView(ofKind elementKind: St func layoutAttributesForDecorationView(ofKind elementKind: Strin func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) - ... var collectionViewContentSize: CGSize { get } ...

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UICollectionViewLayout class UICollectionViewLayout { ... func prepare() func layoutAttributesForElements(in rect: CGRect) -> [UICollecti func layoutAttributesForItem(at indexPath: IndexPath) -> UIColle func layoutAttributesForSupplementaryView(ofKind elementKind: St func layoutAttributesForDecorationView(ofKind elementKind: Strin func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) - ... var collectionViewContentSize: CGSize { get } ...

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UICollectionViewLayout class UICollectionViewLayout { ... func prepare() func layoutAttributesForElements(in rect: CGRect) -> [UICollecti func layoutAttributesForItem(at indexPath: IndexPath) -> UIColle func layoutAttributesForSupplementaryView(ofKind elementKind: St func layoutAttributesForDecorationView(ofKind elementKind: Strin func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) - ... var collectionViewContentSize: CGSize { get } ...

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Wrap up • Collection View Compositional Layouts is incredible! • No need to implement collection view layout subclass • Like just editing configurations • Keep your code simple regardless layout become complex • You can use it now! (without iOS 13)

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Pitfalls

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No Documentation

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2019-09-20 07:14:13.535020+0900 ... [29591:20271214] [CompositionalLayout] Attempting to add contentInsets to an item's dimension along an estimated axis. This layout axis insets will be ignored (however, any non-estimated axis insets will be applied). Please consider using the item's edgeSpacing or the containing group's interItemSpacing instead.

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References • IBPCollectionViewCompositionalLayout
 https://github.com/kishikawakatsumi/IBPCollectionViewCompositionalLayout • App Store.app Clone
 https://github.com/kishikawakatsumi/AppStore-Clone-CollectionViewCompositionalLayouts

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References • Advances in Collection View Layout
 https://developer.apple.com/videos/play/wwdc2019/215/ • All you need to know about UICollectionViewCompositionalLayout
 https://medium.com/flawless-app-stories/all-what-you-need-to-know-about- uicollectionviewcompositionallayout-f3b2f590bdbe • Using CollectionView Compositional Layouts in Swift 5
 https://dev.to/kevinmaarek/using-collectionview-compositional-layouts-in-swift-5-1nan • Move your cells left to right, up and down on iOS 13 — Part 1
 https://medium.com/shopback-engineering/move-your-cells-left-to-right-up-and-down-on- ios-13-part-1-1a5e010f48f9