\n\t![\"StickyHeaderFlowLayout\"](\"/Resources/logo.svg\"){kind=logo}
\n
\n
StickyHeaderFlowLayout\n
Sticky headers for UICollectionView written in pure Swift
\n \n\n\n\nBased on [CSStickyHeaderFlowLayout](https://github.com/CSStickyHeaderFlowLayout/CSStickyHeaderFlowLayout). `StickyHeaderFlowLayout` makes it easy to create sticky headers in `UICollectionView`.\n\n## Integration\n\n#### CocoaPods\n\nYou can use [CocoaPods](http://cocoapods.org/) to install `StickyHeaderFlowLayout` by adding it to your `Podfile`:\n\n```ruby\nplatform :ios, '9.0'\n\ntarget 'MyApp' do\n pod 'StickyHeaderFlowLayout'\nend\n```\n\n#### Manually\n\nTo use this library in your project manually you may:\n\nJust drag `StickyHeaderFlowLayout.swift` and `StickyHeaderFlowLayoutAttributes.swift` to the project tree\n\n## Usage\n\n#### Sample project\n\nRepository contains small sample project which shows basic integration.\n\n#### Basic idea\n\n1. Create layout and collection view\n```swift\nlet layout = StickyHeaderFlowLayout()\nlet collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)\n```\n\n2. Setup sticky header\n```swift\ncollectionView.register(CollectionParallaxHeader.self, forSupplementaryViewOfKind: StickyHeaderFlowLayout.parallaxHeaderIdentifier, withReuseIdentifier: \"parallaxHeader\")\nlayout.parallaxHeaderReferenceSize = CGSize(width: view.frame.size.width, height: 200)\nlayout.parallaxHeaderMinimumReferenceSize = CGSize(width: view.frame.size.width, height: 160)\n```\n\n3. Return correct view in `viewForSupplementaryElementOfKind` function\n```swift\noverride func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {\n if kind == StickyHeaderFlowLayout.parallaxHeaderIdentifier {\n return collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: \"parallaxHeader\", for: indexPath)\n }\n \n // Other views.\n ...\n}\n```\n\n## License\n\n`StickyHeaderFlowLayout` is released under the MIT license. See `LICENSE` for details.\n" }, { "path": "StickyHeaderFlowLayout/Assets/.gitkeep", "content": "" }, { "path": "StickyHeaderFlowLayout/Classes/.gitkeep", "content": "" }, { "path": "StickyHeaderFlowLayout/Classes/StickyHeaderFlowLayout.swift", "content": "//\n// Created by Tsimur Bernikovich on 12/6/18.\n// Copyright © 2018 Tsimur Bernikovich. All rights reserved.\n//\n\nimport UIKit\n\nopen class StickyHeaderFlowLayout: UICollectionViewFlowLayout {\n \n open class var parallaxHeaderIdentifier: String {\n return \"StickyHeaderParallexHeader\"\n }\n private static let headerZIndex = 1024\n \n open var parallaxHeaderReferenceSize: CGSize = .zero\n open var parallaxHeaderMinimumReferenceSize: CGSize = .zero {\n didSet {\n invalidateLayout()\n }\n }\n \n open var parallaxHeaderAlwaysOnTop = false\n open var disableStickyHeaders = false\n open var disableStretching = false\n \n open override func prepare() {\n super.prepare()\n }\n \n open override func initialLayoutAttributesForAppearingSupplementaryElement(ofKind elementKind: String, at elementIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {\n let attributes = super.initialLayoutAttributesForAppearingSupplementaryElement(ofKind: elementKind, at: elementIndexPath)\n if elementKind == type(of: self).parallaxHeaderIdentifier {\n // Sticky header do not need to offset.\n return nil\n } else {\n if var frame = attributes?.frame {\n frame.origin.y = parallaxHeaderReferenceSize.height\n attributes?.frame = frame\n }\n }\n return attributes\n }\n \n open override func finalLayoutAttributesForDisappearingSupplementaryElement(ofKind elementKind: String, at elementIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {\n if elementKind == type(of: self).parallaxHeaderIdentifier {\n let attribute = layoutAttributesForSupplementaryView(ofKind: elementKind, at: elementIndexPath)\n if let attribute = attribute as? StickyHeaderFlowLayoutAttributes {\n updateParallaxHeaderAttribute(attribute)\n }\n return attribute\n } else {\n super.finalLayoutAttributesForDisappearingSupplementaryElement(ofKind: elementKind, at: elementIndexPath)\n }\n return nil\n }\n \n open override func layoutAttributesForSupplementaryView(ofKind elementKind: String, at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {\n var attrubutes = super.layoutAttributesForSupplementaryView(ofKind: elementKind, at: indexPath)\n if attrubutes == nil && elementKind == type(of: self).parallaxHeaderIdentifier {\n attrubutes = StickyHeaderFlowLayoutAttributes(forSupplementaryViewOfKind: elementKind, with: indexPath)\n }\n return attrubutes\n }\n \n open override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {\n guard collectionView?.dataSource != nil else {\n return nil\n }\n \n // The rect should compensate the header size\n var adjustedRect = rect\n adjustedRect.origin.y -= self.parallaxHeaderReferenceSize.height\n \n var allItems: [UICollectionViewLayoutAttributes] = []\n // Perform a deep copy of the attributes returned from super.\n if let originalAttributes = super.layoutAttributesForElements(in: adjustedRect) {\n allItems = originalAttributes.compactMap {\n $0.copy() as? UICollectionViewLayoutAttributes\n }\n }\n \n var headers: [Int: UICollectionViewLayoutAttributes] = [:]\n var lastCells: [Int: UICollectionViewLayoutAttributes] = [:]\n var visibleParallaxHeader = false\n \n for item in allItems {\n let attributes = item\n var frame = attributes.frame\n frame.origin.y += parallaxHeaderReferenceSize.height\n attributes.frame = frame\n \n let indexPath = attributes.indexPath\n let isHeader = attributes.representedElementKind == UICollectionView.elementKindSectionHeader\n let isFooter = attributes.representedElementKind == UICollectionView.elementKindSectionFooter\n \n if isHeader {\n headers[indexPath.section] = attributes\n } else if isFooter {\n // Not implemeneted.\n } else {\n // Get the bottom most cell of that section.\n if let currentAttribute = lastCells[indexPath.section] {\n if indexPath.row > currentAttribute.indexPath.row {\n lastCells[indexPath.section] = attributes\n }\n } else {\n lastCells[indexPath.section] = attributes\n }\n \n if indexPath.item == 0 && indexPath.section == 0 {\n visibleParallaxHeader = true\n }\n }\n \n if isHeader {\n attributes.zIndex = type(of: self).headerZIndex\n } else {\n // For iOS 7.0, the cell zIndex should be above sticky section header.\n attributes.zIndex = 1\n }\n }\n \n if rect.minY <= 0 {\n visibleParallaxHeader = true\n }\n \n if parallaxHeaderAlwaysOnTop {\n visibleParallaxHeader = true\n }\n \n // Create the attributes for the Parallex header.\n if visibleParallaxHeader && parallaxHeaderReferenceSize != .zero {\n let currentAttribute = StickyHeaderFlowLayoutAttributes(forSupplementaryViewOfKind: type(of: self).parallaxHeaderIdentifier, with: IndexPath(index: 0))\n updateParallaxHeaderAttribute(currentAttribute)\n allItems.append(currentAttribute)\n }\n \n if !disableStickyHeaders {\n lastCells.forEach {\n let indexPath = $0.value.indexPath\n let indexPathKey = indexPath.section\n \n if let header = headers[indexPathKey] {\n if header.frame.size != .zero {\n updateHeaderAttributes(header, lastCellAttributes: $0.value)\n }\n } else if let header = layoutAttributesForSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader, at: IndexPath(item: 0, section: indexPath.section)) {\n if header.frame.size != .zero {\n allItems.append(header)\n }\n }\n }\n }\n \n return allItems\n }\n \n open override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {\n let attributes = super.layoutAttributesForItem(at: indexPath)?.copy() as? UICollectionViewLayoutAttributes\n if var frame = attributes?.frame {\n frame.origin.y += parallaxHeaderReferenceSize.height\n attributes?.frame = frame\n }\n return attributes\n }\n \n open override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {\n return true\n }\n \n open override class var layoutAttributesClass: AnyClass {\n return StickyHeaderFlowLayoutAttributes.self\n }\n \n private func updateHeaderAttributes(_ attributes: UICollectionViewLayoutAttributes, lastCellAttributes: UICollectionViewLayoutAttributes) {\n guard let collectionView = collectionView else {\n return\n }\n \n let currentBounds = collectionView.bounds\n attributes.zIndex = type(of: self).headerZIndex\n attributes.isHidden = false\n \n var origin = attributes.frame.origin\n let sectionMaxY = lastCellAttributes.frame.maxY - attributes.frame.size.height\n var y = currentBounds.maxY - currentBounds.size.height + collectionView.contentInset.top\n \n if parallaxHeaderAlwaysOnTop {\n y += parallaxHeaderMinimumReferenceSize.height\n }\n \n origin.y = min(max(y, attributes.frame.origin.y), sectionMaxY)\n attributes.frame = CGRect(origin: origin, size: attributes.frame.size)\n }\n \n private func updateParallaxHeaderAttribute(_ currentAttribute: StickyHeaderFlowLayoutAttributes) {\n guard let collectionView = collectionView else {\n return\n }\n \n var frame = currentAttribute.frame\n frame.size = parallaxHeaderReferenceSize\n \n let bounds = collectionView.bounds\n let maxY = frame.maxY\n \n // Make sure the frame won't be negative values.\n var y = min(maxY - parallaxHeaderMinimumReferenceSize.height, bounds.origin.y + collectionView.contentInset.top)\n let height = max(0, -y + maxY)\n \n let maxHeight = parallaxHeaderReferenceSize.height\n let minHeight = parallaxHeaderMinimumReferenceSize.height\n let progressiveness = (height - minHeight) / (maxHeight - minHeight)\n currentAttribute.progressiveness = progressiveness\n \n // If zIndex < 0 would prevents tap from recognized right under navigation bar.\n currentAttribute.zIndex = 0\n \n // When parallaxHeaderAlwaysOnTop is enabled, we will check when we should update the y position.\n if parallaxHeaderAlwaysOnTop && height <= parallaxHeaderMinimumReferenceSize.height {\n let insetTop = collectionView.contentInset.top\n // Always stick to top but under the nav bar.\n y = collectionView.contentOffset.y + insetTop\n currentAttribute.zIndex = 2000\n }\n \n let normalizedHeight = disableStretching && height > maxHeight ? maxHeight : height\n currentAttribute.frame = CGRect(x: frame.origin.x, y: y, width: frame.size.width, height: normalizedHeight)\n }\n \n}\n\nextension StickyHeaderFlowLayoutAttributes {\n \n override internal var debugDescription: String {\n let indexPathString = \"\\(indexPath.section) \\(indexPath.item)\"\n return \"