在項目中我們經(jīng)常要實現(xiàn)圖片預覽這個功能,簡單的做法就是往scrollview中添加子控件以實現(xiàn)目的,但是一旦要預覽的圖片很多的時候,這樣的做法會創(chuàng)建很多多余的控件,性能上會大打折扣,下面為大家提供一個思路,來解決這種不開心的事情.

思路如下

** 前提我們只需要創(chuàng)建兩個圖片視圖,因為顯示的圖片時候我們只會同時顯示一張圖片,在圖片滑動的時候我們才會同時兩張圖片,照著這樣的思路走下去,首先我們得創(chuàng)建兩個數(shù)組,第一個數(shù)組用于存放已創(chuàng)建為使用的圖形控件對象,第二個用于存放活動中(顯示在屏幕中)的圖形對象.當滑動控件進行滑動的時候,首先檢查緩存數(shù)組中是否對象存在,有則取(取完之后需要移除)無則創(chuàng)建,并且都需要存放在活動中的數(shù)組中,當劃過一頁邊界的時候應當從活動數(shù)組中移除消失在視野中圖形控件并存放在緩存數(shù)組中,以此類推便可.**

下面是代碼實現(xiàn)

let screenBounds = UIScreen.mainScreen().bounds
typealias CallBack = (a:Int,b:Int)->Int
//可循環(huán)利用的ScrollView
class LooperPhoto: UIScrollView,UIScrollViewDelegate{
    
    // 緩存的圖片控件
    var cacheImages = NSMutableArray()
    // 活動的圖片控件
    var actionImages = NSMutableArray()
//    var photos:[JSON]?
    private var dataSources:[AnyObject]?
    var imageType = ImageType.Web
    var pageCount = 0{
        
        didSet{
            if pageCount>oldValue{
               self.contentSize =  CGSizeMake(CGFloat(pageCount)*CGRectGetWidth(self.bounds), 0)
            }
        }
    }

    override init(frame: CGRect) {
       super.init(frame: frame)
       initSetting()

    }

    required init?(coder aDecoder: NSCoder) {
      super.init(coder: aDecoder)
    }
    
    override func awakeFromNib() {
        initSetting()
    }
    
    private func initSetting(){
        self.showsHorizontalScrollIndicator = false
        self.showsVerticalScrollIndicator = false
        self.pagingEnabled = true
        self.delegate = self
    }
    
    func setCurrentPage(page:Int){
        
        self.setContentOffset(CGPointMake(CGFloat(page)*screenBounds.width, 0), animated: false)
     
        
    }

    
    func setImageDataSource(dataSouce:[AnyObject],imageType:ImageType){
        self.pageCount = dataSouce.count
        self.imageType = imageType
        self.dataSources = dataSouce
        showImageAtIndex(0)
    }
    
    
    func showImageAtIndex(index:Int){
     
        var imageView:UIImageView?
        if (cacheImages.count == 0){
          imageView = getImageView(index)
        }else{
          imageView = cacheImages.firstObject as? UIImageView
          imageView?.frame.origin.x = CGFloat(index)*self.bounds.width
          cacheImages.removeObjectAtIndex(0)
        }
        setImageToImageView(index,imageView: imageView!)
        imageView!.tag = index
        actionImages.addObject(imageView!)
        self.addSubview(imageView!)
    }

    
    private func setImageToImageView(index:Int,imageView:UIImageView){
      
        let data:AnyObject = dataSources![index]
        var image:UIImage?
        
        switch imageType{
        case .Local:
          let alAsset =  data as! ALAsset
          image = UIImage(CGImage: alAsset.defaultRepresentation().fullScreenImage().takeUnretainedValue())
        case .Web:
           let imageUrl  = data as! String
           imageView.sd_setImageWithURL(NSURL(string: imageUrl))
        case .Resource:
            let resourceName = data as! String
            image = UIImage(named: resourceName)
        }
        
        if (nil != image){
            imageView.image = image!
        }
    }
    
    func getImageView(index:Int)->UIImageView{
  
        let width = CGRectGetWidth(self.bounds)
        let imageView = UIImageView()
        var frame = self.bounds
        frame.origin.x = CGFloat(index)*width

        imageView.frame = frame
        imageView.contentMode = UIViewContentMode.ScaleAspectFit
        return imageView
    }
    //總共就2個image控件
    func scrollViewDidScroll(scrollView: UIScrollView) {
        
        let scrollViewBounds = scrollView.bounds
        let minX = CGRectGetMinX(scrollViewBounds)
        let maxX = CGRectGetMaxX(scrollViewBounds)
        var firstIndex = Int(minX/scrollViewBounds.width)
        var lastIndex = Int(maxX/scrollViewBounds.width)
        if firstIndex<0{
            firstIndex = 0
        }
        if lastIndex >= pageCount{
            lastIndex = pageCount-1
        }
        
        var tempImagesArrary = [UIImageView]()
        for imageView in actionImages{
            let index = imageView.tag
          
            if index<firstIndex || index>lastIndex{
                imageView.removeFromSuperview()
                tempImagesArrary.append(imageView as! UIImageView)
                cacheImages.addObject(imageView)
            }
        }
        
        for imageView in tempImagesArrary{
            
            actionImages.removeObject(imageView)
        }
        
        //TOO-DO 這里要將不顯示的imageView從ActionImages移除
        for (var i = firstIndex;i<=lastIndex;i++){
            var isShowNewImage = true
            for imageview in actionImages{
                let tagIndex = imageview.tag
                if tagIndex == i{
                   isShowNewImage = false
                }
            }
            if isShowNewImage{
                showImageAtIndex(i)
            }
            
        }
    
    }
    
    enum ImageType{
        
     case Local,Web,Resource
    }
}