Custom Layout for Collection view doesn't update - ios

Question

I am using the following code in order to have a UICollectionView with variable height for various cells:
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return totalItems
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
totalItems -= 1
collectionView.deleteItems(at: [indexPath])
collectionView.collectionViewLayout.invalidateLayout()
}
}
extension InviteViewController : PinterestLayoutDelegate {
// 1. Returns the cell height
func collectionView(_ collectionView: UICollectionView, heightForPhotoAtIndexPath indexPath:IndexPath) -> CGFloat {
print("have: ", indexPath.item)
if(indexPath.item % 3 == 0) {
return 150
} else if(indexPath.item % 3 == 1) {
return 200
} else {
return 250
}
}
}
However I see that the layout doesn't update after the deletion of the UICollectionViewCell and I get errors as:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'UICollectionView received layout attributes for a cell with an index path that does not exist: {length = 2, path = 0 - 7}'
I am stuck and unable to understand why this happens and how to solve this. Please help me find a solution for the same. Thank you.
In case you want to have a look at the layout file I used, please have a look here:
import UIKit
protocol PinterestLayoutDelegate: class {
// 1. Method to ask the delegate for the height of the image
func collectionView(_ collectionView:UICollectionView, heightForPhotoAtIndexPath indexPath:IndexPath) -> CGFloat
}
class PinterestLayout: UICollectionViewLayout {
//1. Pinterest Layout Delegate
weak var delegate: PinterestLayoutDelegate!
//2. Configurable properties
fileprivate var numberOfColumns = 2
fileprivate var cellPadding: CGFloat = 3
//3. Array to keep a cache of attributes.
fileprivate var cache = [UICollectionViewLayoutAttributes]()
//4. Content height and size
fileprivate var contentHeight: CGFloat = 0
fileprivate var contentWidth: CGFloat {
guard let collectionView = collectionView else {
return 0
}
let insets = collectionView.contentInset
return collectionView.bounds.width - (insets.left + insets.right)
}
override var collectionViewContentSize: CGSize {
return CGSize(width: contentWidth, height: contentHeight)
}
override func prepare() {
// 1. Only calculate once
guard cache.isEmpty == true, let collectionView = collectionView else {
return
}
// 2. Pre-Calculates the X Offset for every column and adds an array to increment the currently max Y Offset for each column
let columnWidth = contentWidth / CGFloat(numberOfColumns)
var xOffset = [CGFloat]()
for column in 0 ..< numberOfColumns {
xOffset.append(CGFloat(column) * columnWidth)
}
var column = 0
var yOffset = [CGFloat](repeating: 0, count: numberOfColumns)
// 3. Iterates through the list of items in the first section
for item in 0 ..< collectionView.numberOfItems(inSection: 0) {
let indexPath = IndexPath(item: item, section: 0)
// 4. Asks the delegate for the height of the picture and the annotation and calculates the cell frame.
let photoHeight = delegate.collectionView(collectionView, heightForPhotoAtIndexPath: indexPath)
let height = cellPadding * 2 + photoHeight
let frame = CGRect(x: xOffset[column], y: yOffset[column], width: columnWidth, height: height)
let insetFrame = frame.insetBy(dx: cellPadding, dy: cellPadding)
// 5. Creates an UICollectionViewLayoutItem with the frame and add it to the cache
let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
attributes.frame = insetFrame
cache.append(attributes)
// 6. Updates the collection view content height
contentHeight = max(contentHeight, frame.maxY)
yOffset[column] = yOffset[column] + height
column = column < (numberOfColumns - 1) ? (column + 1) : 0
}
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
var visibleLayoutAttributes = [UICollectionViewLayoutAttributes]()
// Loop through the cache and look for items in the rect
for attributes in cache {
if attributes.frame.intersects(rect) {
visibleLayoutAttributes.append(attributes)
}
}
return visibleLayoutAttributes
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
return cache[indexPath.item]
}
}
I followed: https://www.raywenderlich.com/392-uicollectionview-custom-layout-tutorial-pinterest

Answer 1

override func prepare() {
// 1. Only calculate once
guard cache.isEmpty == true, let collectionView = collectionView else {
return
}
In this part delete guard cache.isEmpty == true,. It works.
extension CategoryPageVC: PinterestLayoutDelegate {
func collectionView(_ collectionView: UICollectionView,
heightForPhotoAtIndexPath indexPath:IndexPath) -> CGFloat {
let rate = self.categoryData[indexPath.item].image.size.width / self.collectionView.frame.size.width * 2
return self.categoryData[indexPath.item].image.size.height / rate
}
}