Swift - UIScrollView 循环滚动

图片循环滚动在 app 上很是常见,网上翻了一些资料,这篇博文 思路蛮不错的,Objective-C写的 参照这个思路自己练习撸了一版 Swift,改进了一下..

效果图:

loopscrollview.png

实现功能

1. 循环滚动
2. 定时自动跳转

当我们设定播放的图片宽度与父视图等宽的话,那么我们只需要准备3个UIView即可满足左右滑动,并且保持当前处于第2个UIView上,可以通过设定contentOffSet处在UIScrollView位置

loopScrollView.contentOffset = CGPoint(x: self.frame.size.width,y: 0)

页面跳转

1. 手动翻页
2. 自动翻页

手动翻页

当我们手动去翻页的时候这里有两种情况:

    //MARK: - UIScrollView delegate
    func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
        let ratio = scrollView.contentOffset.x/self.frame.size.width
        self.endScrollMethod(ratio)
    }
    func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        if !decelerate{
            let ratio = scrollView.contentOffset.x/self.frame.size.width
            self.endScrollMethod(ratio)
        }
    }

• 左右滑动swipe 手势,带有减速效果, scrollViewDidEndDecelerating方法响应
• 左右拖动drag手势,并没有带减速效果,可以根据scrollViewDidEndDragging 方法的decelerate来判断是否有减速效果

当手势动作执行完毕后,就需要做一些处理,根据算出来的ratio来判断向左还是向右,当ratio < 1.0标示向左,反之则向右翻页

private func endScrollMethod(ratio:CGFloat){
        if ratio <= 0.7{
            if currentPage - 1 < 0{
                currentPage = arrImage.count - 1
            }else{
                currentPage -= 1
            }
        }
        if ratio >= 1.3{
            if currentPage == arrImage.count - 1{
                currentPage = 0
            }else{
                currentPage += 1
            }
        }
        self.updateImageData()
        self.startTimer()
    }

根据 currentPage来判断当前处于第几页 而后再更新图片内容

private func updateImageData(){
        if currentPage == 0{
            imageView0.image = arrImage.last
            imageView1.image = arrImage[currentPage]
            imageView2.image = arrImage[currentPage + 1]
        }else if currentPage == arrImage.count - 1{
            imageView0.image = arrImage[currentPage - 1]
            imageView1.image = arrImage[currentPage]
            imageView2.image = arrImage.first
        }else{
            imageView0.image = arrImage[currentPage - 1]
            imageView1.image = arrImage[currentPage]
            imageView2.image = arrImage[currentPage + 1]
        }
        pageControl.currentPage = currentPage
        loopScrollView.contentOffset = CGPoint(x: self.frame.size.width,y: 0)
    }

更新完图片内容后,通过contentOffset将复位当前的位置为第二个 UIView上,至此就完成了翻页动作

自动翻页

启用一个定时器,定时完成以上动作,用一个变量来控制定时器开关

  var autoShow:Bool = false{
        didSet{
            if autoShow{
                self.startTimer()
            }else{
                self.stopTimer()
            }
        }
    }

定时器响应的方法,跳转到下一页 currentPage+1 再更新一下即完成翻页动作

    @objc private func autoTurnNextView(){
        
        if currentPage == arrImage.count - 1{
            currentPage = 0
        }else{
            currentPage += 1
        }
        self.updateImageData()
    } 

初始方法,当设置 arrImage的时候更新视图内容

    var arrImage:[UIImage] = []{
        willSet{
            currentPage = 0
            pageControl.numberOfPages = newValue.count
        }
        didSet{
            self.updateImageData()
        }
    }

使用方法

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    
        let image1 = UIImage(named: "Barcelona0")!
        let image2 = UIImage(named: "Barcelona1")!
        let image3 = UIImage(named: "Barcelona2")!
        let image4 = UIImage(named: "Barcelona3")!
        let images = [image1,image2,image3,image4]
        
        
        let rect = CGRectMake(0, 22, CGRectGetWidth(self.view.frame), CGRectGetWidth(self.view.frame)/16 * 9)
        
        let loopView = CLLoopView(frame:rect)
        self.view.addSubview(loopView)
        loopView.arrImage = images
        loopView.autoShow = true
        loopView.delegate = self
    }

代理方法,当点击scrollview响应的方法,idx为当前页数

    //MARK: - CLLoopView Delegate
    func selectLoopViewPage(idx: Int) {
        print("select page:\(idx)")
    }

GitHub : Demo