collectionview - scaling of center cell before scrolling - ios

Question

I have a vertical collectionView and I am calling a function to scale the centre cell and fade the cells either side. The problem is that it only happens once the scrolling starts. I have tried calling from viewdidload, viewwillappear but can't get this happening before scrolling when the collectionview is first populated.
This is how its being called.
self.collectionView.setScaledDesginParam(scaledPattern: .verticalCenter, maxScale: 1.2, minScale: 0.5, maxAlpha: 1.0, minAlpha: 0.5)
self.collectionView.scaledVisibleCells()
self.collectionView.reloadData()
and this is the main function
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))
}
}

Answer 1

Use below lines of code in viewWillAppear method :
self.collectionView.reloadData()
self.collectionView.setScaledDesginParam(scaledPattern: .verticalCenter, maxScale: 1.2, minScale: 0.5, maxAlpha: 1.0, minAlpha: 0.5)
self.collectionView.scaledVisibleCells()
First reload the collection view and then scale it.