三张图片实现无限轮播

简单描述一下原理

原理其实很简单，只需往scrollerView上放三个imageView即可，初始化时，调整contentOffset，让第二个imageView居中（位于当前屏幕），第一个imageView显示第6张图片（假设是6张），第二个imageView显示第一张图片，第三个imageView显示第二张图片，当手向右滑动时，此时当前屏幕显示的是第6张图片，当滑动动画停止后（代理函数里有），瞬间改变图片（第一个imageView显示第5张图片，第二个imageView显示第6张图片，第三个imageView显示第1张图片），同时改变contentOffset（依然让第二个imageView居中，显示在当前屏幕中），手势向左滑动时同理。

来吧！开整吧！！猿类们都爱用代码说话！！！

• 初始化了一个图片数组，然后是scrollerView的高度，每页的宽度

 view_WIDTH = Double(self.view.frame.width);
 view_HEIGHT = 220.0
 imagesArray = [UIImage.init(named: "James0.jpg")!,UIImage.init(named: "James1.jpg")!,UIImage.init(named: "James2.jpg")!,UIImage.init(named: "James3.jpg")!,UIImage.init(named: "James4.jpg")!,UIImage.init(named: "James5.jpg")!]

• 初始化scrollerView

func loadScrollerView() -> Void {
        
        scrollerView = UIScrollView.init(frame: CGRect.init(x: 0.0, y: 64.0, width: view_WIDTH, height: view_HEIGHT))
        scrollerView.backgroundColor = UIColor.orange
        scrollerView.contentSize = CGSize.init(width: view_WIDTH * 3, height: 0)
        scrollerView.showsVerticalScrollIndicator = false
        scrollerView.showsHorizontalScrollIndicator = false
        scrollerView.isPagingEnabled = true
        scrollerView.bounces = true
        scrollerView.contentOffset = CGPoint.init(x: view_WIDTH, y: 0)
        scrollerView.delegate = self;
        self.view.addSubview(scrollerView)

        imageViewArray = NSMutableArray.init()
        
        for i in 0...2
        {
            let imageView = UIImageView.init()
            imageView.frame = CGRect.init(x: view_WIDTH * Double(i), y: 0.0, width: view_WIDTH, height: view_HEIGHT)
            imageView.contentMode = UIViewContentMode.scaleAspectFill
            imageView.isUserInteractionEnabled = true
            imageView.tag = (5 + i)%6
            print(imageView.tag)
            imageView.image = imagesArray[imageView.tag]
            scrollerView.addSubview(imageView)
            imageViewArray.add(imageView)
            
            let tapGesture = UITapGestureRecognizer.init(target: self, action: #selector(imageViewClicked))
            imageView.addGestureRecognizer(tapGesture)
        }
        
        pageControl = UIPageControl.init(frame: CGRect.init(x: 0.0, y: Double(scrollerView.frame.maxY - 30), width: view_WIDTH, height: 30.0))
        pageControl.numberOfPages = 6
        pageControl.currentPage = 0
        self.view.addSubview(pageControl)
}

• 重新改变图片和contentOffset

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        self.updateImageViewsAndPageControl()
}
    
func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
        self.updateImageViewsAndPageControl()
}

func updateImageViewsAndPageControl() -> Void {
        
        var flag = NSInteger()
        if scrollerView.contentOffset.x > CGFloat(view_WIDTH)
        {
            flag = 1
        }
        else if scrollerView.contentOffset.x == 0.0
        {
            flag = -1
        }
        else
        {
            return
        }
        
        for x in 0..<imageViewArray.count
        {
            let imageView:UIImageView = imageViewArray[x] as! UIImageView
            var index = imageView.tag + flag;
            if index < 0
            {
                index = pageControl.numberOfPages - 1
            }
            else if index >= pageControl.numberOfPages
            {
                index = 0
            }
            imageView.tag = index
            imageView.image = imagesArray[imageView.tag]
        }
        
        let currentImgView:UIImageView = imageViewArray[1] as! UIImageView
        pageControl.currentPage = currentImgView.tag
        
        scrollerView.contentOffset = CGPoint.init(x: view_WIDTH, y: 0)
}