swift 轮播图

引言: swift 轮播图原理
利用UICollectionView , cell0 , cell1 ,cell2 三个cell,
cell 每次滑完之后, 然后刷新数据, 都要再滚动到中间去(不需动画),

图片组: 要显示的图片数组
下标: 图片组的下表
数据源: CollectionView的数据源 (三条数据)

主要代码1:
datas 取图片组里的要显示的三条

 var datas:[String]? {
        var firstIndex = 0;
        var secondIndex = 0
        var thirdIndex = 0;
        
        switch pictures.count {
        case 0:
            return []
        case 1:
            return []
        default:
            firstIndex = (self.index - 1) < 0 ? pictures.count - 1 : self.index - 1
            secondIndex = self.index
            thirdIndex = (self.index + 1) > pictures.count - 1 ? 0 : self.index + 1;
        }
        return [pictures[firstIndex] ,pictures[secondIndex] ,pictures[thirdIndex]];
    }
    
    var index: Int = 0 {
        willSet {
            //print("------------index:\(index)--------------")
        }
        didSet {
            //print("------------index:\(index)--------------");
        }
    }
    
    var pictures:[String] = [] {
        didSet {
            self.collectionV.scrollToItem(at: IndexPath(item: 1, section: 0), at: .left, animated: false)
        }
    }

主要代码2:
滚动的时候,拿正确的下表,并刷新UI,默认滚中间

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        
        var offset: CGFloat = 0
        offset = scrollView.contentOffset.x

        if offset >= self.collectionV.bounds.size.width * 2 {
            if self.index == self.pictures.count - 1 {
                self.index = 0
            }
            else {
                self.index += 1
            }
            print("---------刷新:\(self.index)----------")
            self.collectionV.reloadData();
            self.collectionV.scrollToItem(at: IndexPath(item: 1, section: 0), at: .left, animated: false)
        }
        
        if offset <= 0 {
            if self.index == 0 {
                self.index = self.pictures.count - 1
            }
            else {
                self.index -= 1
            }
            print("---------刷新:\(self.index)----------")
            self.collectionV.reloadData()
            self.collectionV.scrollToItem(at: IndexPath(item: 1, section: 0), at: .left, animated: false)
        }
    }

主要代码3:
UICollectionView 的代理

extension JBKSliderPictureView : UICollectionViewDelegate, UICollectionViewDataSource {
    
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 3;
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell: JBKSliderPictureCell = collectionView.dequeueReusableCell(withReuseIdentifier: "JBKSliderPictureCell", for: indexPath) as! JBKSliderPictureCell;
        cell.nameLabel.text = "---(\(indexPath.item))---"
        cell.imageV.image = UIImage(named: self.datas![indexPath.item]);
        return cell;
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let index = self.index
        print("-------------didSelectItemAt:\(index)---------------")
    }
    
    
}