所要截取的对象
var bg_view: UIView!
截取并且保存的代码如下
UIGraphicsBeginImageContextWithOptions(bg_view.frame.size, false, UIScreen.main.scale)
bg_view.layer.render(in: UIGraphicsGetCurrentContext()!)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
UIImageWriteToSavedPhotosAlbum(image!,self,#selector(image(_:didFinishSavingWithError:contextInfo:)), nil)
结束！
原文：http://www.cnblogs.com/kunH/p/6925176.html