使用UICollectionView实现无限轮播

2938B034999345D234A60E36050EE862.jpg
https://github.com/gsdios/SDCycleScrollView
https://github.com/gsdios/SDCycleScrollView
使用collectionView实现无线轮播的大概思路是一直切换当前的cell（就是一个一个往下滑），当你滑到最后一个的时候让cell马上切换到所有cell的中部（totalItemsCount / 2）然后在数据源中你需要展示的那些数据就依次循环展示（index % self.noticeArray.count，index表示Indexpath.item）
代码只展示切换的逻辑，像collection的创建，layout的创建，代理和数据源就不详细的展示了

//noticeArray表示装有所有数据的数组
var noticeArray : [String]
//这里有collectionViewCell的复用不用考虑性能问题
fileprivate lazy var totalItemsCount:Int = {
            return self.noticeArray.count * 100
    }()

 //设置自动滚动计时器
    func configureAutoScrollTimer() {
        //设置一个定时器，每三秒钟滚动一次
     self.srollTimer = Timer.scheduledTimer(timeInterval: 3, target: self,
                                               selector: #selector(letItScroll),
                                               userInfo: nil, repeats: true)
     RunLoop.main.add(self.srollTimer!, forMode: .commonModes)
    }

 func currentIndex() -> Int {
        if (noticeCollectionView?.frame.size.width == 0 || noticeCollectionView?.frame.size.height == 0) {
            return 0
        }
        var index = 0
     //这里是纵向滑动
        index = Int(((self.noticeCollectionView?.contentOffset.y)! + self.rolllayout.itemSize.height * 0.5) / (self.rolllayout.itemSize.height))
    //横向滑动
//  index = Int(((self.noticeCollectionView?.contentOffset.x)! + self.rolllayout.itemSize.width * 0.5) / (self.rolllayout.itemSize.width))
        return max(0, index)
    }

 func scrollToIndex( targetIndex:inout Int) {
        if targetIndex >= totalItemsCount {
            targetIndex = totalItemsCount / 2
            noticeCollectionView?.scrollToItem(at: IndexPath.init(row: targetIndex, section: 0), at: UICollectionViewScrollPosition.init(rawValue: 0), animated: false)
            return
        }
        noticeCollectionView?.scrollToItem(at: IndexPath.init(row: targetIndex, section: 0), at: UICollectionViewScrollPosition.init(rawValue: 0), animated: true)
    }

    //计时器时间一到
    func letItScroll(){
        if self.totalItemsCount == 0 {
            return
        }
        let currentIndex = self.currentIndex()
        var targetIndex = currentIndex + 1
        self.scrollToIndex(targetIndex: &targetIndex)
    }

 func pageControlIndexWithCurrentCellIndex( index : Int) -> Int {
        return index % self.noticeArray.count
    }

extension AZRollNoticeView : UICollectionViewDelegate{
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let index = self.pageControlIndexWithCurrentCellIndex(index: indexPath.item)
        self.letSelectBlock!(index)
    }
    func scrollViewDidScroll(_ scrollView: UIScrollView){
        let itemIndex = self.currentIndex()
     //当前位置信息
        self.titleCount = self.pageControlIndexWithCurrentCellIndex(index: itemIndex)
    }
    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        self.configureAutoScrollTimer()
    }
    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        self.stopTimer()
    }
}

extension AZRollNoticeView : UICollectionViewDataSource{
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) ->
        UICollectionViewCell {
            self.indexPath = indexPath
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as!AZRollNoticeCell
          let index = self.pageControlIndexWithCurrentCellIndex(index: indexPath.item)
        cell.textLabel?.text = self.noticeArray[index]
        return cell
    }
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return totalItemsCount
    }
}

本文记录自己的理解，有什么不认同的东西直接参考这篇文章
https://github.com/gsdios/SDCycleScrollView