custom collection view not scaling last image - ios

Question

so I have a custom collectionviewflowlayout that works perfectly but in one of my collection views it is not scaling the image as desired. I have attached some images below, you can see that the last cell is not scaling properly.
I'm not sure why this scaling issue is happening in this cell.
the collectionview is a custom class of collectionviewflowlayout which the snapping of cells to the centre of the screen:
class VerticalCollectionViewFlow: UICollectionViewFlowLayout {
override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
if let cv = self.collectionView {
let cvBounds = cv.bounds
let halfHeight = cvBounds.size.height * 0.5
print(proposedContentOffset.y)
let proposedContentOffsetCenterY = proposedContentOffset.y + halfHeight
if let attributesForVisibleCells = self.layoutAttributesForElements(in: cvBounds) {
var candidateAttributes : UICollectionViewLayoutAttributes?
for attributes in attributesForVisibleCells {
// == Skip comparison with non-cell items (headers and footers) == //
if attributes.representedElementCategory != UICollectionElementCategory.cell {
continue
}
if (attributes.center.y == 0) || (attributes.center.y > (cv.contentOffset.y + halfHeight) && velocity.y < 0) {
continue
}
// == First time in the loop == //
guard let candAttrs = candidateAttributes else {
candidateAttributes = attributes
continue
}
let a = attributes.center.y - proposedContentOffsetCenterY
let b = candAttrs.center.y - proposedContentOffsetCenterY
if fabsf(Float(a)) < fabsf(Float(b)) {
candidateAttributes = attributes;
}
}
// Beautification step , I don't know why it works!
if(proposedContentOffset.y == -(cv.contentInset.top)) {
return proposedContentOffset
}
if candidateAttributes != nil {
return CGPoint(x: proposedContentOffset.x, y: floor(candidateAttributes!.center.y - halfHeight))
}
}
}
// fallback
return super.targetContentOffset(forProposedContentOffset: proposedContentOffset)
}
}
and the scaling is handled from another class that is called from viewdidload of the main viewcontroller where the delegates of UIcollectionViewController are set.
import UIKit
public enum SC_ScaledPattern {
case horizontalCenter
case horizontalLeft
case horizontalRight
case verticalCenter
case verticalBottom
case verticalTop
}
open class ScaledVisibleCellsCollectionView {
static let sharedInstance = ScaledVisibleCellsCollectionView()
var maxScale: CGFloat = 1.0
var minScale: CGFloat = 0.5
var maxAlpha: CGFloat = 1.0
var minAlpha: CGFloat = 0.5
var scaledPattern: SC_ScaledPattern = .verticalCenter
}
extension UICollectionView {
/**
Please always set
*/
public func setScaledDesginParam(scaledPattern pattern: SC_ScaledPattern, maxScale: CGFloat, minScale: CGFloat, maxAlpha: CGFloat, minAlpha: CGFloat) {
ScaledVisibleCellsCollectionView.sharedInstance.scaledPattern = pattern
ScaledVisibleCellsCollectionView.sharedInstance.maxScale = maxScale
ScaledVisibleCellsCollectionView.sharedInstance.minScale = minScale
ScaledVisibleCellsCollectionView.sharedInstance.maxAlpha = maxAlpha
ScaledVisibleCellsCollectionView.sharedInstance.minAlpha = minAlpha
}
/**
Please call at any time
*/
public func scaledVisibleCells() {
switch ScaledVisibleCellsCollectionView.sharedInstance.scaledPattern {
case .horizontalCenter, .horizontalLeft, .horizontalRight:
scaleCellsForHorizontalScroll(visibleCells)
break
case .verticalCenter, .verticalTop, .verticalBottom:
self.scaleCellsForVerticalScroll(visibleCells)
break
}
}
}
extension UICollectionView {
fileprivate func scaleCellsForHorizontalScroll(_ visibleCells: [UICollectionViewCell]) {
let scalingAreaWidth = bounds.width / 2
let maximumScalingAreaWidth = (bounds.width / 2 - scalingAreaWidth) / 2
for cell in visibleCells {
var distanceFromMainPosition: CGFloat = 0
switch ScaledVisibleCellsCollectionView.sharedInstance.scaledPattern {
case .horizontalCenter:
distanceFromMainPosition = horizontalCenter(cell)
break
case .horizontalLeft:
distanceFromMainPosition = abs(cell.frame.midX - contentOffset.x - (cell.bounds.width / 2))
break
case .horizontalRight:
distanceFromMainPosition = abs(bounds.width / 2 - (cell.frame.midX - contentOffset.x) + (cell.bounds.width / 2))
break
default:
return
}
let preferredAry = scaleCells(distanceFromMainPosition, maximumScalingArea: maximumScalingAreaWidth, scalingArea: scalingAreaWidth)
let preferredScale = preferredAry[0]
let preferredAlpha = preferredAry[1]
cell.transform = CGAffineTransform(scaleX: preferredScale, y: preferredScale)
cell.alpha = preferredAlpha
}
}
fileprivate func scaleCellsForVerticalScroll(_ visibleCells: [UICollectionViewCell]) {
let scalingAreaHeight = bounds.height / 2
let maximumScalingAreaHeight = (bounds.height / 2 - scalingAreaHeight) / 2
for cell in visibleCells {
var distanceFromMainPosition: CGFloat = 0
switch ScaledVisibleCellsCollectionView.sharedInstance.scaledPattern {
case .verticalCenter:
distanceFromMainPosition = verticalCenter(cell)
break
case .verticalBottom:
distanceFromMainPosition = abs(bounds.height - (cell.frame.midY - contentOffset.y + (cell.bounds.height / 2)))
break
case .verticalTop:
distanceFromMainPosition = abs(cell.frame.midY - contentOffset.y - (cell.bounds.height / 2))
break
default:
return
}
let preferredAry = scaleCells(distanceFromMainPosition, maximumScalingArea: maximumScalingAreaHeight, scalingArea: scalingAreaHeight)
let preferredScale = preferredAry[0]
let preferredAlpha = preferredAry[1]
cell.transform = CGAffineTransform(scaleX: preferredScale, y: preferredScale)
cell.alpha = preferredAlpha
}
}
fileprivate func scaleCells(_ distanceFromMainPosition: CGFloat, maximumScalingArea: CGFloat, scalingArea: CGFloat) -> [CGFloat] {
var preferredScale: CGFloat = 0.0
var preferredAlpha: CGFloat = 0.0
let maxScale = ScaledVisibleCellsCollectionView.sharedInstance.maxScale
let minScale = ScaledVisibleCellsCollectionView.sharedInstance.minScale
let maxAlpha = ScaledVisibleCellsCollectionView.sharedInstance.maxAlpha
let minAlpha = ScaledVisibleCellsCollectionView.sharedInstance.minAlpha
if distanceFromMainPosition < maximumScalingArea {
// cell in maximum-scaling area
preferredScale = maxScale
preferredAlpha = maxAlpha
} else if distanceFromMainPosition < (maximumScalingArea + scalingArea) {
// cell in scaling area
let multiplier = abs((distanceFromMainPosition - maximumScalingArea) / scalingArea)
preferredScale = maxScale - multiplier * (maxScale - minScale)
preferredAlpha = maxAlpha - multiplier * (maxAlpha - minAlpha)
} else {
// cell in minimum-scaling area
preferredScale = minScale
preferredAlpha = minAlpha
}
return [ preferredScale, preferredAlpha ]
}
}
extension UICollectionView {
fileprivate func horizontalCenter(_ cell: UICollectionViewCell)-> CGFloat {
return abs(bounds.width / 2 - (cell.frame.midX - contentOffset.x))
}
fileprivate func verticalCenter(_ cell: UICollectionViewCell)-> CGFloat {
return abs(bounds.height / 2 - (cell.frame.midY - contentOffset.y))
}
}
I have this working on multi collection views, just this one is producing the scaling error.
below is the extension of the collectionview that is handling the sticky nature of the collection/scrollview
extension JourneyViewController: UIScrollViewDelegate {
//------------------------------------------------------------------ make the scrolling a bit sticky
func scrollViewDidScroll(_ scrollView: UIScrollView) {
self.collectionViewPart.scaledVisibleCells()
let offsetY = scrollView.contentOffset.x
let contentHeight = scrollView.contentSize.width
if offsetY > contentHeight - scrollView.frame.size.width {
self.collectionViewPart.reloadData()
}
}
func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
startingScrollingOffset = scrollView.contentOffset
}
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let cellWidth = collectionViewPart.collectionViewLayout.collectionViewContentSize.width
let page: CGFloat
let proposedPage = scrollView.contentOffset.x / cellWidth
// 10% of next cell to change / 90% of previous cell to change
let delta: CGFloat = scrollView.contentOffset.x > startingScrollingOffset.x ? 0.1 : 0.9
if floor(proposedPage + delta) == floor(proposedPage) {
page = floor(proposedPage)
}
else {
page = floor(proposedPage + 1)
}
}
}
hope someone smarter than me can figure this out I've been staring at it for countless hours.
thanks!