Я пытаюсь настроить пользовательский макет collectionView и чувствую, что, возможно, пропускаю шаг.
Я создал collectionView, определил ограничения, изменил макет с потока на пользовательский и выбрал свой собственный класс.
Теперь он не работает и ничего не отображается, поэтому я пытаюсь отладить метод класса, но не могу заставить работать какие-либо операторы печатипотому что никакая функция, кажется, не вызывается.Какой шаг я упускаю при настройке?Вот класс:
import UIKit
class CustomCollectionViewLayout: UICollectionViewLayout {
private var cache = [IndexPath: UICollectionViewLayoutAttributes]()
private var contentWidth = CGFloat()
private var visibleLayoutAttributes = [UICollectionViewLayoutAttributes]()
private var oldBounds = CGRect.zero
private var collectionViewStartY: CGFloat {
guard let collectionView = collectionView else {
return 0
}
return collectionView.bounds.minY
}
private var collectionViewHeight: CGFloat {
return collectionView!.frame.height
}
override public var collectionViewContentSize: CGSize {
return CGSize(width: contentWidth, height: collectionViewHeight)
}
override public func prepare() {
print("calling prepare") //This is what's not printing
guard let collectionView = collectionView,
cache.isEmpty else {
return
}
updateInsets()
collectionView.decelerationRate = .fast
cache.removeAll(keepingCapacity: true)
cache = [IndexPath: UICollectionViewLayoutAttributes]()
oldBounds = collectionView.bounds
var xOffset: CGFloat = 0
var cellWidth: CGFloat = 5
for item in 0 ..< collectionView.numberOfItems(inSection: 0) {
let cellIndexPath = IndexPath(item: item, section: 0)
let cellattributes = UICollectionViewLayoutAttributes(forCellWith: cellIndexPath)
cellattributes.frame = CGRect(x: xOffset, y: 0, width: cellWidth, height: collectionViewHeight)
xOffset = xOffset + cellWidth
contentWidth = max(contentWidth,xOffset)
cache[cellIndexPath] = cellattributes
}
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
visibleLayoutAttributes.removeAll(keepingCapacity: true)
print("layoutattributes called")
for (_, attributes) in cache {
visibleLayoutAttributes.append(self.shiftedAttributes(from: attributes))
}
return visibleLayoutAttributes
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
guard let attributes = cache[indexPath] else { fatalError("No attributes cached") }
print("layoutattributes called")
return shiftedAttributes(from: attributes)
}
override public func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
if oldBounds.size != newBounds.size {
cache.removeAll(keepingCapacity: true)
}
return true
}
override func invalidateLayout(with context: UICollectionViewLayoutInvalidationContext) {
if context.invalidateDataSourceCounts { cache.removeAll(keepingCapacity: true) }
super.invalidateLayout(with: context)
}
}
extension CustomCollectionViewLayout {
func updateInsets() {
guard let collectionView = collectionView else { return }
collectionView.contentInset.left = (collectionView.bounds.size.width - 2.5) / 2
collectionView.contentInset.right = (collectionView.bounds.size.width - 2.5) / 2
}
override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
guard let collectionView = collectionView else { return super.targetContentOffset(forProposedContentOffset: proposedContentOffset) }
let midX: CGFloat = collectionView.bounds.size.width / 2
guard let closestAttribute = findClosestAttributes(toXPosition: proposedContentOffset.x + midX) else { return super.targetContentOffset(forProposedContentOffset: proposedContentOffset) }
return CGPoint(x: closestAttribute.center.x - midX, y: proposedContentOffset.y)
}
private func findClosestAttributes(toXPosition xPosition: CGFloat) -> UICollectionViewLayoutAttributes? {
guard let collectionView = collectionView else { return nil }
let searchRect = CGRect(
x: xPosition - collectionView.bounds.width, y: collectionView.bounds.minY,
width: collectionView.bounds.width * 2, height: collectionView.bounds.height
)
let closestAttributes = layoutAttributesForElements(in: searchRect)?.min(by: { abs($0.center.x - xPosition) < abs($1.center.x - xPosition) })
return closestAttributes
}
private var continuousFocusedIndex: CGFloat {
guard let collectionView = collectionView else { return 0 }
let offset = collectionView.bounds.width / 2 + collectionView.contentOffset.x - 2.5 / 2
return offset / 2.5
}
private func shiftedAttributes(from attributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
guard let attributes = attributes.copy() as? UICollectionViewLayoutAttributes else { fatalError("Couldn't copy attributes") }
let roundedFocusedIndex = round(continuousFocusedIndex)
let focusedItemWidth = CGFloat(20)
if attributes.indexPath.item == Int(roundedFocusedIndex){
attributes.transform = CGAffineTransform(scaleX: 10, y: 1)
} else {
let translationDirection: CGFloat = attributes.indexPath.item < Int(roundedFocusedIndex) ? -1 : 1
attributes.transform = CGAffineTransform(translationX: translationDirection * 20, y: 0)
}
return attributes
}
}
Если класс недействителен, это предотвратит вызов его методов?Что автоматически запускает метод prepare () для макета?
А вот контроллер вида, в котором он используется:
class ViewController: UIViewController, UICollectionViewDelegate,UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 10
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = customCollectionView.dequeueReusableCell(withReuseIdentifier: "singleCell", for: indexPath)
cell.backgroundColor = UIColor.random()
return cell
}
@IBOutlet weak var customCollectionView: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
customCollectionView.delegate = self
}
}