//數(shù)據(jù)源數(shù)組
 let totalCount = 100
 var models: [String] = [String]() {
 didSet {
  //判斷元素個(gè)數(shù)
  if models.count < 2 {
  collectionView.isScrollEnabled = false
  }
  //網(wǎng)上的找來的一個(gè)辦法添加100組數(shù)據(jù)源對應(yīng)的索引數(shù)組indexArr
  for _ in 0..<totalCount {
  for j in 0..<models.count {
   indexArr.append(j)
  }
  }
  //開始就滾動(dòng)到第50組數(shù)據(jù)源
  collectionView.scrollToItem(at: IndexPath(item: totalCount/2 * models.count, section: 0), at: .centeredHorizontally, animated: false)
 }
 }

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
 //找到滾動(dòng)停止的點(diǎn)對應(yīng)的collectionView的indexPath
 let point = self.convert(collectionView.center, to: collectionView)
 let index = collectionView.indexPathForItem(at: point)
 let indexpath = (index?.row ?? 0) % models.count
 
 collectionView.scrollToItem(at: IndexPath(item: totalCount/2 * models.count + indexpath, section: 0), at: .centeredHorizontally, animated: false)
 }

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
 
 //集合視圖的寬高（這里默認(rèn)寬高相等）
 let itemHeight = self.collectionView?.frame.height ?? 0
 //可是視圖內(nèi)的attributes數(shù)組
 let array = super.layoutAttributesForElements(in: rect)
 //item透明度開始變化時(shí)的item的中心點(diǎn)x
 let centerX = self.collectionView!.contentOffset.x + itemHeight/2
 print(self.collectionView?.contentOffset.x ?? 0)
 
 for attributes in array! {
  //開始變化時(shí)的item的中心點(diǎn)x 與 實(shí)際中心點(diǎn)相比較
  let value = attributes.center.x - centerX
  let delta = abs(value)
  //設(shè)置縮放比例，此處4*itemHeight可根據(jù)縮放效果進(jìn)行修改
  let scale = 1 - delta/(4*itemHeight)
 
  //設(shè)置縮放比例
  attributes.transform = CGAffineTransform.init(scaleX: scale, y: scale)
  //層次關(guān)系，設(shè)置此屬性使item依次上下排列
  attributes.zIndex = Int(1 - abs(delta))
  
  //value<=0表示向左移動(dòng)，最前面的item停止一段距離
  if value <= 0{
  //實(shí)際中心點(diǎn)與開始變化時(shí)的item的中心點(diǎn)小于等于設(shè)定的邊界值
  if delta >= 0 && delta <= itemHeight
  {
   //item的中心點(diǎn)固定不變
   attributes.center.x = centerX
   //根據(jù)推進(jìn)值，改變item的透明度，此處的delta>10是想讓item有一個(gè)達(dá)到目標(biāo)區(qū)域時(shí)有一個(gè)停頓效果而不是直接進(jìn)入改變透明度的階段
   attributes.alpha = (delta > 10) ? (1 - delta/(itemHeight/4)) : 1
   //設(shè)置縮放比例，停頓階段不進(jìn)行縮放
   attributes.transform = CGAffineTransform.init(scaleX: 1, y: 1)
  } else {
   //移動(dòng)大于邊界值，就是從停頓階段到透明度改變，此處是下一個(gè)item上來,當(dāng)前item透明度變?yōu)?
   attributes.alpha = 0
  }
  }
 }
 return array
 }

override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
 
 let targetRect = CGRect(x: proposedContentOffset.x, y: 0.0, width: self.collectionView!.bounds.size.width, height: self.collectionView!.bounds.size.height)
 
 //目標(biāo)區(qū)域中包含的cell
 let attrArray = super.layoutAttributesForElements(in: targetRect) as! [UICollectionViewLayoutAttributes]
 //collectionView落在屏幕重點(diǎn)的x坐標(biāo)
 let horizontalCenterX = proposedContentOffset.x + (self.collectionView?.frame.height ?? 0)/2
 var offsetAdjustment = CGFloat(MAXFLOAT)
 for layoutAttributes in attrArray {
  
  let itemHorizontalCenterX = layoutAttributes.center.x
  //找出離中心店最近的
  if (abs(itemHorizontalCenterX-horizontalCenterX) < abs(offsetAdjustment)) {
  offsetAdjustment = itemHorizontalCenterX - horizontalCenterX
  }
 }
 
 //返回collectionView最終停留的位置
 return CGPoint(x: proposedContentOffset.x + offsetAdjustment, y: proposedContentOffset.y)
 
 }
//當(dāng)collectionView的顯示范圍發(fā)生改變的時(shí)候，是否重新布局
 override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
 return true
 }