UICollectionView collant en-tête dans swift

La dernière solution que j'ai trouvé:

À l'aide de cette coutume disposition de flux, il était possible de résoudre ce collant en-tête:

class StickyHeaderCollectionViewFlowLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
var superAttributes: [UICollectionViewLayoutAttributes]? = super.layoutAttributesForElementsInRect(rect) as? [UICollectionViewLayoutAttributes]
if superAttributes == nil {
//If superAttributes couldn't cast, return
            return super.layoutAttributesForElementsInRect(rect)
}
let contentOffset = collectionView!.contentOffset
var missingSections = NSMutableIndexSet()
for layoutAttributes in superAttributes! {
if (layoutAttributes.representedElementCategory == .Cell) {
if let indexPath = layoutAttributes.indexPath {
missingSections.addIndex(layoutAttributes.indexPath.section)
}
}
}
for layoutAttributes in superAttributes! {
if let representedElementKind = layoutAttributes.representedElementKind {
if representedElementKind == UICollectionElementKindSectionHeader {
if let indexPath = layoutAttributes.indexPath {
missingSections.removeIndex(indexPath.section)
}
}
}
}
missingSections.enumerateIndexesUsingBlock { idx, stop in
let indexPath = NSIndexPath(forItem: 0, inSection: idx)
if let layoutAttributes = self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: indexPath) {
superAttributes!.append(layoutAttributes)
}
}
for layoutAttributes in superAttributes! {
if let representedElementKind = layoutAttributes.representedElementKind {
if representedElementKind == UICollectionElementKindSectionHeader {
let section = layoutAttributes.indexPath!.section
let numberOfItemsInSection = collectionView!.numberOfItemsInSection(section)
let firstCellIndexPath = NSIndexPath(forItem: 0, inSection: section)!
let lastCellIndexPath = NSIndexPath(forItem: max(0, (numberOfItemsInSection - 1)), inSection: section)!
let (firstCellAttributes: UICollectionViewLayoutAttributes, lastCellAttributes: UICollectionViewLayoutAttributes) = {
if (self.collectionView!.numberOfItemsInSection(section) > 0) {
return (
self.layoutAttributesForItemAtIndexPath(firstCellIndexPath),
self.layoutAttributesForItemAtIndexPath(lastCellIndexPath))
} else {
return (
self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: firstCellIndexPath),
self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionFooter, atIndexPath: lastCellIndexPath))
}
}()
let headerHeight = CGRectGetHeight(layoutAttributes.frame)
var origin = layoutAttributes.frame.origin
origin.y = min(contentOffset.y, (CGRectGetMaxY(lastCellAttributes.frame) - headerHeight))
//Uncomment this line for normal behaviour:
                    //origin.y = min(max(contentOffset.y, (CGRectGetMinY(firstCellAttributes.frame) - headerHeight)), (CGRectGetMaxY(lastCellAttributes.frame) - headerHeight))

layoutAttributes.zIndex = 1024
layoutAttributes.frame = CGRect(origin: origin, size: layoutAttributes.frame.size)
}
}
}
return superAttributes
}
override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
return true
}
}

Créer une mise en page où les en-têtes sont collants classiques, modifier cette ligne:

origin.y = min(contentOffset.y, (CGRectGetMaxY(lastCellAttrs.frame) - headerHeight))

à cette ligne:

origin.y = min(max(contentOffset.y, (CGRectGetMinY(firstCellAttrs.frame) - headerHeight)), (CGRectGetMaxY(lastCellAttrs.frame) - headerHeight))

Espérant que ce est utile pour les autres!

Mise à jour

Mis à jour pour corriger un crash (merci à Robert Atkins!) et certaines mises à jour de Swift 1.2

tvOS & iOS 9

tvOS et iOS 9 introduit la propriété sectionHeadersPinToVisibleBounds qui peut être utilisé

Je fixe mon accident en essais pour les essais de sections vides comme suggéré dans ce gist. J'ai également ajouté un couple de if lets pour plus de Swift points de style ;-). Maintenant cela fonctionne pour moi:

class StickyHeaderCollectionViewFlowLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
var answer: [UICollectionViewLayoutAttributes] = super.layoutAttributesForElementsInRect(rect)! as [UICollectionViewLayoutAttributes]
let contentOffset = collectionView!.contentOffset
var missingSections = NSMutableIndexSet()
for layoutAttributes in answer {
if (layoutAttributes.representedElementCategory == .Cell) {
if let indexPath = layoutAttributes.indexPath {
missingSections.addIndex(layoutAttributes.indexPath.section)
}
}
}
for layoutAttributes in answer {
if let representedElementKind = layoutAttributes.representedElementKind {
if representedElementKind == UICollectionElementKindSectionHeader {
if let indexPath = layoutAttributes.indexPath {
missingSections.removeIndex(indexPath.section)
}
}
}
}
missingSections.enumerateIndexesUsingBlock { idx, stop in
let indexPath = NSIndexPath(forItem: 0, inSection: idx)
if let layoutAttributes = self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: indexPath) {
answer.append(layoutAttributes)
}
}
for layoutAttributes in answer {
if let representedElementKind = layoutAttributes.representedElementKind {
if representedElementKind == UICollectionElementKindSectionHeader {
let section = layoutAttributes.indexPath!.section
let numberOfItemsInSection = collectionView!.numberOfItemsInSection(section)
let firstCellIndexPath = NSIndexPath(forItem: 0, inSection: section)!
let lastCellIndexPath = NSIndexPath(forItem: max(0, (numberOfItemsInSection - 1)), inSection: section)!
let (firstCellAttributes: UICollectionViewLayoutAttributes, lastCellAttributes: UICollectionViewLayoutAttributes) = {
if (self.collectionView!.numberOfItemsInSection(section) > 0) {
return (
self.layoutAttributesForItemAtIndexPath(firstCellIndexPath),
self.layoutAttributesForItemAtIndexPath(lastCellIndexPath))
} else {
return (
self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: firstCellIndexPath),
self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionFooter, atIndexPath: lastCellIndexPath))
}
}()
let headerHeight = CGRectGetHeight(layoutAttributes.frame)
var origin = layoutAttributes.frame.origin
origin.y = min(max(contentOffset.y, (CGRectGetMinY(firstCellAttributes.frame) - headerHeight)), (CGRectGetMaxY(lastCellAttributes.frame) - headerHeight))
layoutAttributes.zIndex = 1024
layoutAttributes.frame = CGRect(origin: origin, size: layoutAttributes.frame.size)
}
}
}
return answer
}
override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
return true
}
}

Voici une solution simple qui fonctionne si vous avez seulement une section.

class StickyHeaderLayout: UICollectionViewFlowLayout {
override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
return true
}
override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
var attributes = super.layoutAttributesForElementsInRect(rect)! as! [UICollectionViewLayoutAttributes]
let offset          = collectionView?.contentOffset
for attrs in attributes {
if attrs.representedElementKind == nil {
let indexPath        = NSIndexPath(forItem: 0, inSection: attrs.indexPath.section)
let layoutAttributes = self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: indexPath)
attributes.append(layoutAttributes)
}
}
for attrs in attributes {
if attrs.representedElementKind == nil {
continue
}
if attrs.representedElementKind == UICollectionElementKindSectionHeader {
var headerRect = attrs.frame
headerRect.size.height = headerHeight
headerRect.origin.y = offset!.y
attrs.frame = headerRect
attrs.zIndex = 1024
break
}
}
return attributes
}
}

Swift 3 version en essayant d'éviter les ! où il fait sens.

class StickyHeaderCollectionViewFlowLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
guard var superAttributes = super.layoutAttributesForElements(in: rect), let collectionView = collectionView else {
return super.layoutAttributesForElements(in: rect)
}
let collectionViewTopY = collectionView.contentOffset.y + collectionView.contentInset.top
let contentOffset = CGPoint(x: 0, y: collectionViewTopY)
let missingSections = NSMutableIndexSet()
superAttributes.forEach { layoutAttributes in
if layoutAttributes.representedElementCategory == .cell && layoutAttributes.representedElementKind != UICollectionElementKindSectionHeader {
missingSections.add(layoutAttributes.indexPath.section)
}
}
missingSections.enumerate(using: { idx, stop in
let indexPath = IndexPath(item: 0, section: idx)
if let layoutAttributes = self.layoutAttributesForSupplementaryView(ofKind: UICollectionElementKindSectionHeader, at: indexPath) {
superAttributes.append(layoutAttributes)
}
})
for layoutAttributes in superAttributes {
if let representedElementKind = layoutAttributes.representedElementKind {
if representedElementKind == UICollectionElementKindSectionHeader {
let section = layoutAttributes.indexPath.section
let numberOfItemsInSection = collectionView.numberOfItems(inSection: section)
let firstCellIndexPath = IndexPath(item: 0, section: section)
let lastCellIndexPath = IndexPath(item: max(0, (numberOfItemsInSection - 1)), section: section)                   
let cellAttributes:(first: UICollectionViewLayoutAttributes, last: UICollectionViewLayoutAttributes) = {
if (collectionView.numberOfItems(inSection: section) > 0) {
return (
self.layoutAttributesForItem(at: firstCellIndexPath)!,
self.layoutAttributesForItem(at: lastCellIndexPath)!)
} else {
return (
self.layoutAttributesForSupplementaryView(ofKind: UICollectionElementKindSectionHeader, at: firstCellIndexPath)!,
self.layoutAttributesForSupplementaryView(ofKind: UICollectionElementKindSectionFooter, at: lastCellIndexPath)!)
}
}()
let headerHeight = layoutAttributes.frame.height
var origin = layoutAttributes.frame.origin
//This line makes only one header visible fixed at the top
//                   origin.y = min(contentOffset.y, cellAttributes.last.frame.maxY - headerHeight)
                    //Uncomment this line for normal behaviour:
                    origin.y = min(max(contentOffset.y, cellAttributes.first.frame.minY - headerHeight), cellAttributes.last.frame.maxY - headerHeight)
layoutAttributes.zIndex = 1024
layoutAttributes.frame = CGRect(origin: origin, size: layoutAttributes.frame.size)
}
}
}
return superAttributes
}
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
return true
}
}