通過UIViewControllerAnimatedTransitioning實現(xiàn)圖片的轉(zhuǎn)場動畫，效果類似手機自帶的照片查看器。詳細過程如下：
先看看效果：

QQ20180507-223238-HD.gif

首先造一個ShowImageController控制器

class ShowImageController: UIViewController {

}

那么它能做什么，首先要能展示圖片，給它一個UIImageView

class ShowImageController: UIViewController {
/// 圖像視圖
    private lazy var imageView: UIImageView = {
        let iv = UIImageView()
        
        return iv
    }()
}
    

其次，它還要支持縮放，給它一個UIScrollView

class ShowImageController: UIViewController {
    /// 圖像視圖
    private lazy var imageView: UIImageView = {
        let iv = UIImageView()
        
        return iv
    }()
    /// 滾動視圖
    private lazy var scrollView: UIScrollView = {
        let s = UIScrollView(frame: self.view.bounds)
        s.backgroundColor = UIColor.black
        // 支持縮放
        // 1. 設(shè)置代理
        s.delegate = self
        // 2. 最小大縮放比例
        s.minimumZoomScale = 1
        s.maximumZoomScale = 2.0
        
        return s
    }()
}

添加一個構(gòu)造方法

• 捕捉一個屏幕快照dummyView
• 設(shè)置transitioningDelegate

init(sourceView:UIImageView) {
    super.init(nibName: nil, bundle: nil)
    
    self.setImage(image: sourceView.image)
    let window = UIApplication.shared.keyWindow
    self.showPicDelegate.dummyView = sourceView.snapshotView(afterScreenUpdates: false)
    self.showPicDelegate.sourceRect = sourceView.convert(sourceView.bounds, to: window)
    self.showPicDelegate.destRect = imageSize(sourceView.image!)
    self.transitioningDelegate = self.showPicDelegate
    modalPresentationStyle = UIModalPresentationStyle.custom
}

然后實現(xiàn)transitioningDelegate，新建ShowPicAnimator類，添加屬性

class ShowPicAnimator: NSObject, UIViewControllerTransitioningDelegate, UIViewControllerAnimatedTransitioning {
    ///是開始還是結(jié)束
    var isPresent: Bool = true
    ///快照
    var dummyView: UIView?
    ///起始位置
    var sourceRect: CGRect = CGRect.zero
    ///結(jié)束位置
    var destRect: CGRect = CGRect.zero
}

添加代理方法

// 指定誰負責轉(zhuǎn)場動畫
func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    isPresent = true
    return self
}
func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    isPresent = false
    return self
}
//UIViewControllerAnimatedTransitioning
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
    return 0.3
}
/* self實現(xiàn)動畫
1. 計算動畫的起始位置
2. 計算動畫的目標位置
*/
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
}

具體實現(xiàn)細節(jié)見代碼