Swift UIScrollView图片缩放

1. 布局
   UIScrollView上加UIImageView，拉好约束

2. 图片比例缩放

//拿到图片高度
let hImage = kScreenW*image.size.height/image.size.width
layoutIconH.constant = hImage

3. 添加双击手势

//2. 双击
let dTap = UITapGestureRecognizer(target: self, action: #selector(handleDoubleTap(_:)))
dTap.numberOfTapsRequired = 2
ivIcon.addGestureRecognizer(dTap

@objc fileprivate func handleDoubleTap(_ ges: UITapGestureRecognizer) {
    
    guard let vGes = ges.view else {
        return
    }
    
    let newScale = isScaled ? 1 : sv.zoomScale*1.5
    let zoomRect = zoomRectForScale(newScale, center: ges.location(in: vGes))
    
    isScaled = !isScaled
    
    sv.zoom(to: zoomRect, animated: true)
}

fileprivate func zoomRectForScale(_ scale: CGFloat, center: CGPoint) -> CGRect {
    var zoomRect = CGRect.zero
    zoomRect.size.height = sv.height/scale
    zoomRect.size.width = sv.width/scale
    
    zoomRect.origin.x = center.x-(zoomRect.width*0.5)
    zoomRect.origin.y = center.y-(zoomRect.height*0.5)

    return zoomRect
}

3. UIScrollView代理方法

func scrollViewDidEndZooming(_ scrollView: UIScrollView, with view: UIView?, atScale scale: CGFloat) {
    scrollView.setZoomScale(scale, animated: false)
}

//返回要缩放的UIImageView
func viewForZooming(in scrollView: UIScrollView) -> UIView? {
    return ivIcon
}