外面只需要一行代碼就可以點(diǎn)擊查看大圖，再次點(diǎn)擊縮放放回原圖扳剿。

先定義一個(gè)顯示圖片的ShowHelper類(lèi)---本來(lái)想用struct的旁趟，但是貌似不支持添加手勢(shì)，只有放棄了庇绽。锡搜。橙困。。耕餐。
我現(xiàn)在是能用struct就用struct凡傅，很少用class了，來(lái)看一下struct的優(yōu)點(diǎn)---swift.gg上面的

struct優(yōu)點(diǎn).png

//放大圖片的時(shí)間
private let showBigDuration = 0.6
//縮放圖片的時(shí)間
private let showOriginalDuration = 0.6
class ShowHelper: NSObject {
    /// 圖片imageView的原始frame
   private static var originalFrame = CGRect()
    private override init() {
        super.init()
    }
}

然后寫(xiě)一個(gè)extension----（為了干凈整潔蛾方，我定義類(lèi)/結(jié)構(gòu)體的時(shí)候，只寫(xiě)屬性）上陕，其它方法桩砰，我全部放在extension里面---只給外面提供一個(gè)show(imageView: UIImageView)方法，其它全部是private私有方法

extension ShowHelper {
//類(lèi)方法
    class func show(imageView: UIImageView) {
       imageView.userInteractionEnabled = true
        
        let tap = UITapGestureRecognizer(target: self, action: #selector(showBigImage(_:)))
        imageView.addGestureRecognizer(tap)
    }
   
    //private私有方法释簿。亚隅。。
   @objc private class func showBigImage(sender: UITapGestureRecognizer) {
//swift里面我不喜歡用強(qiáng)制解析(!)----套用一句話----你每用一個(gè)庶溶！煮纵，就會(huì)殺死一只貓
//同時(shí)也為了去掉金字塔類(lèi)型的判斷。偏螺。行疏。我用guard / guard let來(lái)代替if/ if let 
    guard let imageV = sender.view as? UIImageView else {
        fatalError("it is not UIImageView")
    }
    guard let image = imageV.image else {
        return
    }
    guard let window = UIApplication.sharedApplication().delegate?.window else {
        return
    }
//originalFrame重新歸零
    originalFrame = CGRect()
    let oldFrame = imageV.convertRect(imageV.bounds, toView: window)
    let backgroundView = UIView(frame: UIScreen.mainScreen().bounds)
    backgroundView.backgroundColor = UIColor.blackColor()
    backgroundView.alpha = 0.0
//賦值originalFrame
    originalFrame = oldFrame
    let newImageV = UIImageView(frame: oldFrame)
    newImageV.contentMode = .ScaleAspectFit
    newImageV.image = image
    backgroundView.addSubview(newImageV)
    window?.addSubview(backgroundView)
    
    UIView.animateWithDuration(showBigDuration) {
        let width = UIScreen.mainScreen().bounds.size.width
        let height = image.size.height * width / image.size.width
        let y = (UIScreen.mainScreen().bounds.size.height - image.size.height * width / image.size.width) * 0.5
        newImageV.frame = CGRectMake(0, y, width, height)
        backgroundView.alpha = 1
    }
    let tap2 = UITapGestureRecognizer(target: self, action: #selector(ShowHelper.showOriginal(_:)))
    backgroundView.addGestureRecognizer(tap2)
    }
    //private私有方法。套像。酿联。
    @objc private class func showOriginal(sender: UITapGestureRecognizer) {
        guard let backgroundView = sender.view else {
            return
        }
        guard let imageV = backgroundView.subviews.first else {
            return
        }
//大圖的frame變?yōu)樵瓉?lái)的frame，backgroundView的透明度為0夺巩，同時(shí)backgroundView從父視圖移除
        UIView.animateWithDuration(showOriginalDuration, animations: {
            imageV.frame = originalFrame
            backgroundView.alpha = 0.0
            }) { finished in
                backgroundView.removeFromSuperview()
        }
    }
}