Swift实现无限轮播效果

import UIKit

class CycleScrollView: UIView, UICollectionViewDelegate,UICollectionViewDataSource {

  var bottomView : UICollectionView?
  var width : CGFloat?
  var height : CGFloat?
  var timer : Timer?
  
  override init(frame: CGRect){
    
    super.init(frame: frame)
    // 1.设置背景色
    self.backgroundColor = UIColor.clear
    // 2.设置宽高
    width = self.frame.size.width
    height = self.frame.size.height
    // 3.添加bottomView
    setupBottomView()
    // 4.添加定时器
    setupTimer()
  }
  required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
  
  
  func setupBottomView() {
    
    // 5.设置collectionView的布局
    let flowLayout = UICollectionViewFlowLayout();
    flowLayout.itemSize = self.bounds.size
    flowLayout.minimumLineSpacing = 0;
    flowLayout.minimumInteritemSpacing = 0;
    flowLayout.scrollDirection = UICollectionViewScrollDirection.horizontal;
    bottomView = UICollectionView.init(frame: self.bounds, collectionViewLayout: flowLayout)
    self.addSubview(bottomView!);
    // 6.设置collectionView的尺寸
    bottomView?.contentSize = CGSize(width:width! * CGFloat(4),height:height!)
    // 7.分页
    bottomView?.isPagingEnabled = true
    // 8.去掉滚动条
    bottomView?.showsVerticalScrollIndicator = false
    bottomView?.showsHorizontalScrollIndicator = false
    // 9.设置代理
    bottomView?.delegate = self
    bottomView?.dataSource = self
    // 10.注册cell
    bottomView?.register(UICollectionViewCell().classForCoder, forCellWithReuseIdentifier: "ID");
    if #available(iOS 10.0, *) {
      // 11.预加载
      bottomView?.isPrefetchingEnabled = true
    } else {
      // Fallback on earlier versions
    }
  }
  func setupTimer() {
    // 12.实例化定时器
    timer = Timer.init(timeInterval: 2, target: self, selector: #selector(timerAction), userInfo: nil, repeats: true);
    RunLoop.main.add(timer!, forMode: RunLoopMode.defaultRunLoopMode);

    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 2) {
    
      self.timer?.fire();
    }
  }
  func timerAction() {
    
    var contentOffsetX = (self.bottomView?.contentOffset.x)! + self.frame.size.width
    
    if contentOffsetX > self.frame.size.width * 3 {
      // 当前视图显示的是第三个的时候，设置bottomView的偏移量为0
      self.bottomView?.contentOffset = CGPoint(x:0,y:0)
      contentOffsetX = self.frame.size.width
    }
     self.bottomView?.setContentOffset(CGPoint(x:contentOffsetX,y:0), animated: true)
  }
  // 重写removeFromSuperview方法，用于删除定时器，否则定时器一直存在，浪费内存
  override func removeFromSuperview() {
    
    timer?.invalidate()
    timer = nil
    super.removeFromSuperview()
  }
  // Mark:UICollectionViewDataSource
  // 设置Itmes
  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    
    return 4;
  }
  // 设置cell
  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    
    let cell : UICollectionViewCell = collectionView.dequeueReusableCell(withReuseIdentifier: "ID", for: indexPath)
    for view : UIView in cell.contentView.subviews {
      
      view.removeFromSuperview()
    }
    let imageView = UIImageView.init(frame: cell.contentView.bounds)
    if indexPath.row < 3 {
      
      imageView.image = UIImage.init(named: String(indexPath.row))

    } else {
      imageView.image = UIImage.init(named: String(0))
    }
    cell.contentView.addSubview(imageView)
    
    return cell;
  }
  // Mark:UICollectionViewDelegate
  // 点击方法
  func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    
    print("您点击了第 \(indexPath.row == 3 ? 0 : indexPath.row) 个");
  }
  
}