// MARK: - 设置数据源
  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
//    print(self.arrayM.count)
    return self.arrayM.count * 3
  }

if collectionView.contentOffset.x == CGFloat(3 * self.arrayM.count - 1) * self.collectionView.bounds.width {
      self.collectionView.contentOffset.x = CGFloat(self.arrayM.count - 1) * self.collectionView.bounds.width
    }

if collectionView.contentOffset.x == 0 {
      self.collectionView.contentOffset.x = CGFloat(2 * self.arrayM.count - 1) * self.collectionView.bounds.width
      
    }

import UIKit

class ViewController: UIViewController ,UICollectionViewDataSource, UICollectionViewDelegate {

  @IBOutlet weak var collectionView: UICollectionView!
  var timer : Timer?
  var arrayM : [BOModel] = [] {
    didSet {
      self.collectionView.reloadData()
    }
  }
  static let CellID = "cell"
  override func viewDidLoad() {
    super.viewDidLoad()
    
    self.collectionView.dataSource = self
    self.collectionView.delegate = self

    // 加载数据
    loadData()
    self.collectionView.register(UINib.init(nibName: "BOCollectionViewCell", bundle: nil), forCellWithReuseIdentifier: ViewController.CellID)
    
    //设置collextionView
    setupCollectionView()
    
    // 开启定时器
    starTimer()
    
  }

  /// 从polist中加载数据
  func loadData() {
    let stemp: NSArray = NSArray(contentsOfFile: Bundle.main.path(forResource: "shops.plist", ofType: nil)!)!
    
    for dict in stemp {
      let model = BOModel.init(dict: dict as! [String : Any])
      
      self.arrayM.append(model)
    }
  }
  /// 设置cellection的布局方式
  ///
  /// - Returns: 一个布局类型
  func setupCollectionFlowlayout() -> (UICollectionViewFlowLayout) {
    let flowLayout = UICollectionViewFlowLayout()
    flowLayout.itemSize = self.collectionView.bounds.size
    flowLayout.minimumLineSpacing = 0
    flowLayout.minimumInteritemSpacing = 0
    flowLayout.scrollDirection = .horizontal
    flowLayout.sectionInset = UIEdgeInsetsMake(0, 0, 0, 0)
    return flowLayout
  }
  
  /// 设置collectionVIew
  func setupCollectionView() -> () {
    
    self.collectionView.collectionViewLayout = self.setupCollectionFlowlayout()
    self.collectionView.showsVerticalScrollIndicator = false
    self.collectionView.showsHorizontalScrollIndicator = false
    self.collectionView.isPagingEnabled = true
    
  }
  
  // MARK: - 设置数据源
  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
//    print(self.arrayM.count)
    return self.arrayM.count * 3
  }
  
  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = self.collectionView.dequeueReusableCell(withReuseIdentifier: ViewController.CellID, for: indexPath) as! BOCollectionViewCell
    
    cell.model = self.arrayM[indexPath.row % self.arrayM.count]
    return cell
  }
  
  // MARK: - 实现代理方法
  func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    //contentOffset.x == 0 时,重新设置contentOffset.x的值
    if collectionView.contentOffset.x == 0 {
      self.collectionView.contentOffset.x = CGFloat(2 * self.arrayM.count - 1) * self.collectionView.bounds.width
      
    }
    //当到达最后一个cell时,重新设置contentOffset.x的值
    if collectionView.contentOffset.x == CGFloat(3 * self.arrayM.count - 1) * self.collectionView.bounds.width {
      self.collectionView.contentOffset.x = CGFloat(self.arrayM.count - 1) * self.collectionView.bounds.width
    }
    
  }
  
  
  /// 开启定时器
  func starTimer () {
    let timer = Timer.init(timeInterval: 1, target: self, selector: #selector(ViewController.nextPage), userInfo: nil, repeats: true)
    // 这一句代码涉及到runloop 和 主线程的知识,则在界面上不能执行其他的UI操作
    RunLoop.main.add(timer, forMode: RunLoopMode.commonModes)
    
    self.timer = timer
    
  }
  
  /// 在1秒后,自动跳转到下一页
  func nextPage() {
    // 如果到达最后一个,则变成第四个
    if collectionView.contentOffset.x == CGFloat(3 * self.arrayM.count - 1) * self.collectionView.bounds.width {
      self.collectionView.contentOffset.x = CGFloat(self.arrayM.count - 1) * self.collectionView.bounds.width
    }else {
      // 每过一秒,contentOffset.x增加一个cell的宽度
      self.collectionView.contentOffset.x += self.collectionView.bounds.size.width
    }

}
  
  
  /// 当collectionView开始拖动的时候,取消定时器
  func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
    self.timer?.invalidate()
    self.timer = nil
  }
  
  /// 当用户停止拖动的时候,开启定时器
  func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    starTimer()
  }
}

import UIKit

class BOCollectionViewCell: UICollectionViewCell {

  @IBOutlet weak var imageView: UIImageView!
  var model : BOModel? {
    didSet {
      guard let image = UIImage.init(named: (model?.name)!) else {
        return
      }
      
      
      self.imageView.image = image
    }
  }
  override func awakeFromNib() {
    super.awakeFromNib()
 
  }

}

import UIKit

class BOCollectionViewCell: UICollectionViewCell {

  @IBOutlet weak var imageView: UIImageView!
  var model : BOModel? {
    didSet {
      guard let image = UIImage.init(named: (model?.name)!) else {
        return
      }
      
      
      self.imageView.image = image
    }
  }
  override func awakeFromNib() {
    super.awakeFromNib()
 
  }

}