collectionview - масштабирование центральной ячейки до прокрутки

Question

У меня есть вертикаль collectionView, и я вызываю функцию масштабирования центральной ячейки и выцветаю ячейки с каждой стороны. Проблема в том, что это происходит только после запуска прокрутки. Я пробовал звонить от viewdidload, viewwillappear, но это не может произойти до прокрутки, когда сначала заполняется collectionview. Вот как его зовут.

self.collectionView.setScaledDesginParam(scaledPattern: .verticalCenter, maxScale: 1.2, minScale: 0.5, maxAlpha: 1.0, minAlpha: 0.5) 
self.collectionView.scaledVisibleCells() 
self.collectionView.reloadData() 

и это является основной функцией

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

Использование ниже строк кода в методе viewWillAppear:

self.collectionView.reloadData() 
self.collectionView.setScaledDesginParam(scaledPattern: .verticalCenter, maxScale: 1.2, minScale: 0.5, maxAlpha: 1.0, minAlpha: 0.5) 
self.collectionView.scaledVisibleCells() 

Первый перезагрузить вид коллекции, а затем масштабировать его.