UIGraphicsBeginImageContextWithOptionsCGSizeMakeselfbackViewframesizewidthselfbackViewframesizeheight NO 00; currentView 当前的view 创建一个基于位图的图形上下文并指定大小为 selfbackViewlayer renderInContextUIGraphicsGe

UIGraphicsBeginImageContextWithOptions(CGSize(width: self.backView.frame.size.width, height: self.backView.frame.size.height), false, 0.0) //currentView 当前的view 创建一个基于位图的图形上下文并指定大小为 self.backView.layer.render(in: UIGraphicsGetCurrentContext()!) //renderInContext呈现接受者及其子范围到指定的上下文 let viewImage = UIGraphicsGetImageFromCurrentImageContext()! //返回一个基于当前图形上下文的图片 UIGraphicsEndImageContext() //移除栈顶的基于当前位图的图形上下文 return viewImage