Swift圖片輪播

• 效果圖

• 核心思想
  一個(gè)UIScrollView，三個(gè)UIImageView，一個(gè)[UIImage]（至少兩張圖片）
  ScrollView的ContentOffset等于三倍屏幕寬,ImageView在ScrollView上的位置始終固定,當(dāng)滾動(dòng)時(shí)修改各自對(duì)應(yīng)的圖片，滾動(dòng)完成后將Scrollview的ContentOffset置于中間，這樣就形成圖片循環(huán)輪播的”假象”。
  左滑示意圖：
  
  
  右滑示意圖：
  
  
  核心代碼如下：

private func updateImage() {
        if currentPage == 0 {
            leftImageView.image   = imageArray.last
            centerImageView.image = imageArray[currentPage]
            rightImageView.image  = imageArray[currentPage + 1]
        } else if currentPage == imageArray.count - 1 {
            leftImageView.image   = imageArray[currentPage - 1]
            centerImageView.image = imageArray[currentPage]
            rightImageView.image  = imageArray.first
        } else {
            leftImageView.image   = imageArray[currentPage - 1]
            centerImageView.image = imageArray[currentPage]
            rightImageView.image  = imageArray[currentPage + 1]
        }
        if let completeOperate = operate {
            completeOperate(page: currentPage)
        }
        pageControl.currentPage = currentPage
        scrollView.setContentOffset(CGPoint(x: width, y: 0), animated: false)
    }

• 具體實(shí)現(xiàn)過(guò)程
  本文是封裝了一個(gè)繼承于UIView的類(lèi)，需要的時(shí)候直接拿出來(lái)用就行了。
  屬性

    private var scrollView      = UIScrollView()
    private var pageControl     = UIPageControl()
    private var leftImageView   = UIImageView()
    private var centerImageView = UIImageView()
    private var rightImageView  = UIImageView()
    private var currentPage     = 0
    private var width: CGFloat!
    private var height: CGFloat!
    private var timer: NSTimer?
    /// 滾動(dòng)方向
    enum RollingDirection : Int {
        case Left
        case Right
    }
    /// 指示器當(dāng)前頁(yè)顏色
    var currentPageIndicatorTintColor:UIColor = .whiteColor(){
        willSet{
            pageControl.currentPageIndicatorTintColor = newValue
        }
    }
    /// 指示器顏色
    var pageIndicatorTintColor:UIColor = .whiteColor(){
        willSet{
            pageControl.pageIndicatorTintColor = newValue
        }
    }
    /// 是否自動(dòng)滾動(dòng)
    var autoRoll = false {
        willSet {
            if newValue {
                startTimer()
            } else {
                stopTimer()
            }
        }
    }
    /// 滾動(dòng)方向
    var direction: RollingDirection = .Right {
        willSet {
            stopTimer()
        }
        didSet {
            if autoRoll {
                startTimer()
            }
        }
    }
    /// 間隔時(shí)間
    var timeInterval: NSTimeInterval = 3 {
        willSet {
            stopTimer()
        }
        didSet {
            if autoRoll {
                startTimer()
            }
        }
    }
    /// 圖片數(shù)組
    var imageArray: [UIImage] = [] {
        willSet {
            stopTimer()
            currentPage = 0
            pageControl.numberOfPages = newValue.count
        }
        didSet {
            updateImage()
            if autoRoll {
                startTimer()
            }
        }
    }

    /// 滾動(dòng)完成響應(yīng)事件
    var operate: ((page: Int)->())?

自定義構(gòu)造函數(shù)，使用時(shí)可以選擇是否自動(dòng)滾動(dòng)，滾動(dòng)時(shí)間和方向等

    /**
     自定義構(gòu)造函數(shù)
     - parameter frame:                 frame
     - parameter isAutoRoll:            是否自動(dòng)滾動(dòng)
     - parameter rollDirection:         滾動(dòng)方向
     - parameter timeInt:               滾動(dòng)時(shí)間間隔
     - parameter images:                圖片數(shù)組
     - parameter scrollCompleteOperate: 滾動(dòng)完成響應(yīng)事件,參數(shù)page為當(dāng)前頁(yè)數(shù)
     */
    init(frame: CGRect,
         isAutoRoll: Bool?,
         rollDirection: RollingDirection?,
         timeInt: NSTimeInterval?,
         images:[UIImage],
         scrollCompleteOperate:((page: Int)->())?) {
        super.init(frame: frame)
        initializeUserInterface()

        imageArray = images
        pageControl.numberOfPages = imageArray.count
        if let autoR = isAutoRoll {
            autoRoll = autoR
        }
        if let direct = rollDirection {
            direction = direct
        }
        if let timeI = timeInt {
            timeInterval = timeI
        }
        if let completeOperate = scrollCompleteOperate {
            operate = completeOperate
        }
        //初始化
        updateImageData()
        startTimer()
    }

重寫(xiě)父類(lèi)構(gòu)造函數(shù)

    //重寫(xiě)父類(lèi)初始化方法
    override init(frame: CGRect) {
        super.init(frame: frame)
        initializeUserInterface()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        fatalError("init(coder:) has not been implemented")

    }

定時(shí)器相關(guān)，這里使用自定義類(lèi)來(lái)創(chuàng)建定時(shí)器，下文會(huì)提到，防止定時(shí)器循環(huán)引用導(dǎo)致視圖控制器不能被釋放

    //啟動(dòng)定時(shí)器
    private func startTimer() {
        timer = nil
        //調(diào)用自定義對(duì)象，讓timer對(duì)其進(jìn)行強(qiáng)引用，而不對(duì)視圖控制器強(qiáng)引用
        timer = WeakTimerObject.scheduledTimerWithTimeInterval(timeInterval, aTargat: self, aSelector: #selector(pageRoll), userInfo: nil, repeats: true)
    }

    //關(guān)閉定時(shí)器
    private func stopTimer() {
        if let _ = timer?.valid {
            timer?.invalidate()
            timer = nil
        }
    }

    //定時(shí)器觸發(fā)方法
    @objc private func pageRoll() {
        switch direction {
        case .Left:
            scrollView.setContentOffset(CGPoint(x: 0, y: 0), animated: true)
        case .Right:
            scrollView.setContentOffset(CGPoint(x: width * 2, y: 0), animated: true)
        }
    }

滑動(dòng)方向判斷，無(wú)論是手動(dòng)滑動(dòng)還是自動(dòng)滑動(dòng)都要判斷左滑還是右滑

    //判斷向左滑動(dòng)還是向右滑動(dòng)
    private func judgeDirection(ratio: CGFloat) {
        if ratio < 1 {
            if currentPage == 0 {
                currentPage = imageArray.count - 1
            } else {
                currentPage -= 1
            }
        } else if ratio > 1 {
            if currentPage == imageArray.count - 1 {
                currentPage = 0
            } else {
                currentPage += 1
            }
        }
        updateImage()
    }

實(shí)現(xiàn)ScrollView協(xié)議方法

    //MARK:-scrollViewDelegate
    //手動(dòng)滑動(dòng)停止調(diào)用
    func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
        judgeDirection(scrollView.contentOffset.x / width)
    }
    //自動(dòng)滑動(dòng)停止調(diào)用
    func scrollViewDidEndScrollingAnimation(scrollView: UIScrollView) {
        judgeDirection(scrollView.contentOffset.x / width)
    }

• 使用操作
  1.調(diào)用自定義構(gòu)造函數(shù)

        let imageRollView = ImageScrollView(frame: CGRect(x: 0, y: 64, width: SCREEN_WIDTH, height: SCREEN_HEIGHT - 64),
                                            isAutoRoll: true,
                                            rollDirection: .Right,
                                            timeInt: 4,
                                            images: ary) { (page) in
                                                print("第\(page)頁(yè)")
        }
        self.view.addSubview(imageRollView)

2.調(diào)用默認(rèn)構(gòu)造函數(shù)

        let imageRollView          = ImageScrollView(frame: CGRect(x: 0, y: 64, width: SCREEN_WIDTH, height: SCREEN_HEIGHT - 64))
        imageRollView.imageArray   = ary
        imageRollView.autoRoll     = true
        imageRollView.timeInterval = 3
        imageRollView.direction    = .Left
        imageRollView.operate      = {(page) in
            print("第\(page)頁(yè)")
        }
        self.view.addSubview(imageRollView)

定時(shí)器問(wèn)題

• 問(wèn)題描述
  Demo完成后檢查發(fā)現(xiàn)問(wèn)題，在VC中開(kāi)啟定時(shí)器，圖片輪播正常，并在析構(gòu)函數(shù)中將定時(shí)器移除：

deinit {
    if let _ = timer?.valid {
            timer?.invalidate()
            timer = nil
            print("停止定時(shí)器")
       }
}

正常情況下，VC出棧后會(huì)自動(dòng)釋放內(nèi)存并調(diào)用deinit()函數(shù)，然而問(wèn)題出現(xiàn)了，VC出棧后并沒(méi)有調(diào)用deinit()函數(shù)，這就意味VC并沒(méi)有釋放，定時(shí)器一直處于開(kāi)啟狀態(tài)：

• 解決方法
  解決問(wèn)題的核心是打破循環(huán)引用。本文解決方法是創(chuàng)建一個(gè)類(lèi)，在類(lèi)中實(shí)現(xiàn)定時(shí)器scheduledTimerWithTimeInterval()方法，創(chuàng)建定時(shí)器的時(shí)候就使用該類(lèi)來(lái)創(chuàng)建，目的是讓NSTimer的target為該類(lèi)的對(duì)象，而不是視圖控制器，這樣NSTimer對(duì)該類(lèi)對(duì)象進(jìn)行強(qiáng)引用，而不對(duì)視圖控制器進(jìn)行強(qiáng)引用，這樣就打破循環(huán)引用這個(gè)環(huán)了。
  1.構(gòu)造一個(gè)scheduledTimerWithTimeInterval()方法：

class WeakTimerObject: NSObject {
    weak var targat: AnyObject?
    var selector: Selector?
    var timer: NSTimer?
    static func scheduledTimerWithTimeInterval(interval: NSTimeInterval,
                                               aTargat: AnyObject,
                                               aSelector: Selector,
                                               userInfo: AnyObject?,
                                               repeats: Bool) -> NSTimer {
        let weakObject      = WeakTimerObject()
        weakObject.targat   = aTargat
        weakObject.selector = aSelector
        weakObject.timer    = NSTimer.scheduledTimerWithTimeInterval(interval,
                                                                  target: weakObject,
                                                                  selector: #selector(fire),
                                                                  userInfo: userInfo,
                                                                  repeats: repeats)
        return weakObject.timer!
    }

2.將WeakTimerObject的對(duì)象設(shè)置為NSTimer的target，并響應(yīng)定時(shí)器方法

    func fire(ti: NSTimer) {
        if let _ = target {
            targat?.performSelector(selector!, withObject: ti.userInfo)
        } else {
            timer?.invalidate()
        }
    }
}

• Demo下載
  Swift圖片無(wú)限輪播