滚动banner复习

实现思路

无论有多少张滚动图片,UIScrollView只有三张图片显示. scrollView的contentOffset始终保持在中间图片, 当向左或者向右滚动一张图片结束后, 重新设置contentOffset在中间图片位置, 并重新设置imageView里面的image. 以达到图片滚动的效果.

import UIKit

class PageScrollView: UIView {
    
    private let imageViewMaxCount = 3 //scrollview最大图片数
    private var imageScrollView: UIScrollView!
    private var pageControl: UIPageControl!
    private var timer: NSTimer?
    private var placeholderImage: UIImage?
    private var imageClick:((index: Int) -> ())?  //图片点击回调
    //传入scrollview图片data
    var headData: HeadResources? {
        didSet {
            //设置data后, 先停止滚动
            if timer != nil {
                timer!.invalidate()
                timer = nil
            }
            
            if headData?.count >= 0 {
                //设置pagecontrol的page数量, 并设置从0开始滚动
                pageControl.numberOfPages = (headData?.count)!
                pageControl.currentPage = 0
                //重置scrollview的contentoffset并且设置imageview的图片
                updatePageScrollView()
                //开始自动滚动
                startTimer()
            }
        }
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        buildImageScrollView()
        
        buildPageControl()
        
    }
    
    convenience init(frame: CGRect, placeholder: UIImage, focusImageViewClick:((index: Int) -> Void)){
        self.init(frame: frame)
        placeholderImage = placeholder
        imageClick = focusImageViewClick
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    // MARK: (3)设置scrollview和pageControl的位置和尺寸, 并设置scrollview中imageview位置和尺寸
    override func layoutSubviews() {
        super.layoutSubviews()
        
        imageScrollView.frame       = bounds
        imageScrollView.contentSize = CGSizeMake(CGFloat(imageViewMaxCount) * width, 0)
        //设置scrollview中imageview位置和尺寸
        for i in 0...imageViewMaxCount - 1 {
            let imageView   = imageScrollView.subviews[i] as! UIImageView
            imageView.userInteractionEnabled = true
            imageView.frame = CGRectMake(CGFloat(i) * imageScrollView.width, 0, imageScrollView.width, imageScrollView.height)
        }
        
        let pageW: CGFloat = 80
        let pageH: CGFloat = 20
        let pageX: CGFloat = imageScrollView.width  - pageW
        let pageY: CGFloat = imageScrollView.height - pageH
        pageControl.frame  = CGRectMake(pageX, pageY, pageW, pageH)
        
        updatePageScrollView()
    }
    
    // MARK: (1)创建scrollview
    private func buildImageScrollView() {
        imageScrollView = UIScrollView()
        imageScrollView.bounces = false
        imageScrollView.showsHorizontalScrollIndicator = false
        imageScrollView.showsVerticalScrollIndicator = false
        imageScrollView.pagingEnabled = true
        imageScrollView.delegate = self
        addSubview(imageScrollView)
        
        //添加imageview,并添加点击手势
        for _ in 0..<3 {
            let imageView = UIImageView()
            let tap = UITapGestureRecognizer(target: self, action: "imageViewClick:")
            imageView.addGestureRecognizer(tap)
            imageScrollView.addSubview(imageView)
        }
    }
    
    // MARK: (2)创建pageControl
    private func buildPageControl() {
        pageControl = UIPageControl()
        pageControl.hidesForSinglePage = true
        pageControl.pageIndicatorTintColor = UIColor(patternImage: UIImage(named: "v2_home_cycle_dot_normal")!)
        pageControl.currentPageIndicatorTintColor = UIColor(patternImage: UIImage(named: "v2_home_cycle_dot_selected")!)
        addSubview(pageControl)
    }
    
    // A - 第一步标记imageview.tag来标记image的位置 (判断的根据是currentpage)
    //如果有5张image, 第一次显示的时候, currentpage = 0, 三个imageview.tag分别为4,0,1
    //第二次显示时, currentpage = 1 , 三个imageview.tag分别为0,1,2
    private func updatePageScrollView() {
        for var i = 0; i < imageScrollView.subviews.count; i++ {    
            let imageView = imageScrollView.subviews[i] as! UIImageView

            //拿到当前页位置
            var index = pageControl.currentPage
            
            if i == 0 {
                //第一个image, index-1
                index--
            } else if 2 == i { //最多就三个imageview,也有可能就两个或一个
                //第三个image, index+1
                index++
            }
            
            if index < 0 {
                index = self.pageControl.numberOfPages - 1
            } else if index >= pageControl.numberOfPages {
                index = 0
            }
            
            //标记imageview中image所在的位置
            imageView.tag = index
            if headData?.focus?.count > 0 {
                imageView.sd_setImageWithURL(NSURL(string: headData!.focus![index].img!), placeholderImage: placeholderImage)
            }
        }
        
        //始终设置contentOffset在中间一个imageview
        imageScrollView.contentOffset = CGPointMake(imageScrollView.width, 0)
    }
    
    //timer
    private func startTimer() {
        timer = NSTimer(timeInterval: 3.0, target: self, selector: "next", userInfo: nil, repeats: true)
        NSRunLoop.mainRunLoop().addTimer(timer!, forMode: NSRunLoopCommonModes)
    }
    
    private func stopTimer() {
        timer?.invalidate()
        timer = nil
    }
    
    func next() {
        imageScrollView.setContentOffset(CGPointMake(2.0 * imageScrollView.frame.size.width, 0), animated: true)
    }
    
    // action
    func imageViewClick(tap: UITapGestureRecognizer) {
        if imageClick != nil {
            imageClick!(index: tap.view!.tag)
        }
    }
}

// MARK:- UIScrollViewDelegate
extension PageScrollView: UIScrollViewDelegate {
    
    //scrollview滚动一半时设置pagecontrol.  
    //B - 第一次(4,0,1)如果向下滚动一张时, 滚动到一半后, currentpage变为1
    func scrollViewDidScroll(scrollView: UIScrollView) {
        var page: Int = 0
        var minDistance: CGFloat = CGFloat(MAXFLOAT)
        for i in 0..

}