Ios UICollectionViewCell上的比例转换

我有一个垂直滚动的集合视图，我想在滚动发生时使中心单元格变大

我在收藏视图中使用无限滚动

以下是我的自定义流布局：

import Foundation
import InfiniteLayout
class CustomLayout: InfiniteLayout {

    public override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        let attributes = super.layoutAttributesForElements(in: rect).flatMap {
            self.copyLayoutAttributes(from: $0)
        }
        guard let visibleRect = self.visibleCollectionViewRect() else {
            return attributes
        }
        let centeredOffset = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
        for attributes in attributes ?? [] {
            let diff = self.scrollDirection == .horizontal ? centeredOffset.x - attributes.center.x : centeredOffset.y - attributes.center.y
            let distance = abs(diff)
            let tolerance : CGFloat = 0.02
            var scale = 1.00 + tolerance - (( distance / centeredOffset.y ) * 0.105)
            if(scale > 1.0){
                scale = 1.0
            }
            if(scale < 0.460091){
                scale = 0.460091
            }
            attributes.transform = attributes.transform.scaledBy(x: scale, y: scale)
            attributes.alpha = changeSizeScaleToAlphaScale(scale)
        }
        return attributes
    }

    func changeSizeScaleToAlphaScale(_ x : CGFloat) -> CGFloat {
        let minScale : CGFloat = 0.46
        let maxScale : CGFloat = 1.0

        let minAlpha : CGFloat = 0.25
        let maxAlpha : CGFloat = 1.0

        return ((maxAlpha - minAlpha) * (x - minScale)) / (maxScale - minScale) + minAlpha
    }
}

这是我滚动到可见单元格的扩展：

extension InfiniteCollectionView {

    func scrollToNearestVisibleCollectionViewCell() {
        self.decelerationRate = UIScrollView.DecelerationRate.normal
        let visibleCenterPositionOfScrollView = Float(self.contentOffset.y + (self.bounds.size.height / 2))
        var closestCellIndex = -1
        var closestDistance: Float = .greatestFiniteMagnitude
        for i in 0..<self.visibleCells.count {
            let cell = self.visibleCells[i]
            let cellHeight = cell.bounds.size.width
            let cellCenter = Float(cell.frame.origin.y + cellHeight / 2)

            // Now calculate closest cell
            let distance: Float = fabsf(visibleCenterPositionOfScrollView - cellCenter)
            if distance < closestDistance {
                closestDistance = distance
                closestCellIndex = self.indexPath(for: cell)!.row
            }
        }
        if closestCellIndex != -1 {
            self.scrollToItem(at: IndexPath(row: closestCellIndex, section: 0), at: .centeredVertically, animated: true)
        }
    }
}

扩展无限集合视图{
func scrollToNearestVisibleCollectionViewCell（）函数{
self.decelerationRate=UIScrollView.decelerationRate.normal
让visibleCenterPositionOfScrollView=Float（self.contentOffset.y+（self.bounds.size.height/2））
var closestCellIndex=-1
var closestDistance:Float=.greatestfinitemagnity
对于0中的i..我不确定这是否是最好的方法

在收集视图
中间做一个var跟踪索引
    var index = IndexPath()


在VIEWDIDLAUT子视图中，一旦计算出了已配置的布局
无效，则检查中间的单元格。
 override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        let center = self.view.convert(collectionView.center, to: collectionView)
        index = collectionView.indexPathForItem(at: center) ?? IndexPath(item: 0, section: 0)
        collectionView.collectionViewLayout.invalidateLayout()
    }

然后在SizeFormitem

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        if index.count != 0  {
            if index.item == indexPath.item {
                return CGSize(width: collectionView.frame.size.width, height: 100)
            }

        }
        return CGSize(width: collectionView.frame.size.width, height: 50)
    }

然后在scrollviewdidscroll中再次调用ViewDidLayoutSubView，以便重新计算居中元素并更改项目大小

func scrollViewDidScroll(_ scrollView: UIScrollView) {

        viewDidLayoutSubviews()
    }

谢谢，但是我通过定制我的流程布局来实现这个概念！这是唯一正确的方法
func scrollViewDidScroll(_ scrollView: UIScrollView) {

        viewDidLayoutSubviews()
    }