Configuring dynamic cell height with a custom collection view layout swift - ios

Question

I have a custom collection view layout which loads the cells from the bottom up for a messaging app, except I'm having trouble implementing dynamic cell heights. I believe the protocol and delegates I hooked up to retrieve the dynamic cell height are working for each cell (which I deduced from printing the height for each indexPath.item) except when the collectionView is loaded the cell heights are not the heights they are supposed to be. They are all just one static height (not the 80 preset by var cellHeight) and show just one line of text.
protocol InvertedStackProtocol: class {
func collectionView(_ collectionView: UICollectionView, heightForCellAtIndexPath indexPath: IndexPath) -> CGFloat
}
class InvertedStackLayout: UICollectionViewLayout, UICollectionViewDelegateFlowLayout {
var cellHeight: CGFloat = 80
weak var delegate: InvertedStackProtocol!
override func prepare() {
guard let collectionView = self.collectionView else {return}
for item in 0 ..< collectionView.numberOfItems(inSection: 0) {
let indexPath = IndexPath(item: item, section: 0)
let height = delegate.collectionView(collectionView, heightForCellAtIndexPath: indexPath)
print (height, indexPath.item)
cellHeight = height
}
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
var layoutAttrs = [UICollectionViewLayoutAttributes]()
if let collectionView = self.collectionView {
for section in 0 ..< collectionView.numberOfSections {
if let numberOfSectionItems = numberOfItemsInSection(section) {
for item in 0 ..< numberOfSectionItems {
let indexPath = IndexPath(item: item, section: section)
let layoutAttr = layoutAttributesForItem(at: indexPath)
if let layoutAttr = layoutAttr, layoutAttr.frame.intersects(rect) {
layoutAttrs.append(layoutAttr)
}
}
}
}
}
return layoutAttrs
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
let layoutAttr = UICollectionViewLayoutAttributes(forCellWith: indexPath)
let contentSize = self.collectionViewContentSize
layoutAttr.frame = CGRect(
x: 0, y: contentSize.height - CGFloat(indexPath.item + 1) * cellHeight,
width: contentSize.width, height: cellHeight)
return layoutAttr
}
func numberOfItemsInSection(_ section: Int) -> Int? {
if let collectionView = self.collectionView,
let numSectionItems = collectionView.dataSource?.collectionView(collectionView, numberOfItemsInSection: section)
{
return numSectionItems
}
return 0
}
override var collectionViewContentSize: CGSize {
get {
var height: CGFloat = 0.0
var bounds = CGRect.zero
if let collectionView = self.collectionView {
for section in 0 ..< collectionView.numberOfSections {
if let numItems = numberOfItemsInSection(section) {
height += CGFloat(numItems) * cellHeight
}
}
bounds = collectionView.bounds
}
return CGSize(width: bounds.width, height: max(height, bounds.height))
// return CGSize(width: bounds.width, height: height) do this for more exact fit of collection view
}
}
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
if let oldBounds = self.collectionView?.bounds,
oldBounds.width != newBounds.width || oldBounds.height != newBounds.height
{
return true
}
return false
}
}

Answer 1

Use this method to change the height, UICollectionViewCell.
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: 125.0, height: 175.0)
}