UICollectionViewCell sizeForItemAt values being reverted to fitItemSize somehow? - ios

Question

I have set up 2 collectionView in a viewcontroller, both get their data from an endpoint and then reloadData().
One collectionView act like an header tab and have its cell size depend on its intritic size and rely on insetForSection to position/align the cell in the center of the collectionView.
Another have "sort-of" fixed size for themselves where the first cell will be almost the entire width of the collectionView and then the cells after the first one will occupy semi-half the collectionView width.
I have setted-up delegate and extension methods, however for some reason the sizeforItem that focus on the second CollectionView doesn't "stick", they get reverted. When i do :
self.statusOptionCollectionView.reloadData()
self.statusOptionCollectionView.performBatchUpdates({
self.statusOptionCollectionView.layoutIfNeeded()
}) { (complete) in
debugPrint("Batch Update complete")
}
I saw a brief frame of my desired outcome but then the collectionView suddenly undo my sizeForItem code and change the cell to something akin to "size-to-fit". (Pics: Below).
Question is how do i fix this? What is causing this? Is it because i have 2 collectionView in one viewcontroller? I've tried to invalidatingLayout in viewdidlayoutsubviews but it doesn't work. "I did use storyboard but i already delete the collectionView and re-add it, didn't fix it)
I want Something Like This (Focus one the second viewcontroller layout) :
My CollectionView Layout Code is Like This (kindTabCollectionView is the "header", with center alignment) :
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
if collectionView.isEqual(self.kindTabCollectionView){
let layout = collectionViewLayout as! UICollectionViewFlowLayout
let totalCellWidth = layout.itemSize.width * CGFloat(self.kindArray.count)
let totalSpacingWidth = CGFloat(8 * (self.kindArray.count - 1))
let leftInset = (collectionView.bounds.size.width - CGFloat(totalCellWidth + totalSpacingWidth)) / 2
let rightInset = leftInset
return UIEdgeInsets(top: 0, left: leftInset, bottom: 0, right: rightInset)
}else{
return UIEdgeInsets(top: 8, left: 8, bottom: 8, right: 8)
}
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
if collectionView.isEqual(self.kindTabCollectionView){
let flowLayout = collectionViewLayout as! UICollectionViewFlowLayout
return flowLayout.itemSize
}else{
let height = CGFloat(40.0)
let flowLayout = collectionViewLayout as! UICollectionViewFlowLayout
let widthMargin = (flowLayout.sectionInset.left + flowLayout.sectionInset.left + flowLayout.minimumInteritemSpacing)
if indexPath.item == 0 && indexPath.section == 0{
let width = floor(collectionView.frame.size.width - widthMargin)
return CGSize(width: width, height: height)
}else{
let width = floor((collectionView.frame.size.width / 2) - widthMargin)
return CGSize(width: width, height: height)
}
}
}
However, the result that come out is this :
(Sorry, it was just a few frame, i tried my best to screen shot it, but it did tried to change to correct frame size, but then it just revert to the small "fitToSize" pic)

Answer 1

Check collectionView's "Estimated Size" attribute in the Size Inspector (Storyboard). It should be set to "None" when using an extension of UICollectionViewDelegateFlowLayout to set cell's size.
As stated in the Xcode 11 Release Notes:
Cells in a UICollectionView can now self size with Auto Layout
constrained views in the canvas. To opt into the behavior for existing
collection views, enable “Automatic” for the collection view’s
estimated size, and “Automatic” for cell’s size from the Size
inspector. If deploying before iOS 13, you can activate self sizing
collection view cells by calling performBatchUpdates(_:completion:)
during viewDidLoad(). (45617083)
So, newly created collectionViews have the attribute "Estimated Size" set as "Automatic" and the cell's size is computed considering its subview dimensions, thus ignoring the UICollectionViewDelegateFlowLayout extension methods, even though they are called.