swift 截图扩展

extension UIView{
    //将当前视图转为UIImage
    func asImage() -> UIImage {
        let renderer = UIGraphicsImageRenderer(bounds: bounds)
        return renderer.image { rendererContext in
            layer.render(in: rendererContext.cgContext)
        }
    }
    public func snapshot(rect: CGRect = CGRect.zero, scale: CGFloat = UIScreen.main.scale) -> UIImage? {
        var snapRect = rect
        if __CGSizeEqualToSize(rect.size, CGSize.zero) {
            snapRect = calculateSnapshotRect()
        }
        UIGraphicsBeginImageContextWithOptions(snapRect.size, false, scale)
        defer {
            UIGraphicsEndImageContext()
        }
        let siF = self.drawHierarchy(in: snapRect, afterScreenUpdates: false)
        if !siF {
            self.drawHierarchy(in: snapRect, afterScreenUpdates: true)
        }
        
        print("siF == \(siF)")
        return UIGraphicsGetImageFromCurrentImageContext()
    }
    // 计算UIView所显示内容Rect
    func calculateSnapshotRect() -> CGRect {
        var targetRect = self.bounds
        if let scrollView = self as? UIScrollView {
            let contentInset = scrollView.contentInset
            let contentSize = scrollView.contentSize
            
            targetRect.origin.x = contentInset.left
            targetRect.origin.y = contentInset.top
            targetRect.size.width = targetRect.size.width  - contentInset.left - contentInset.right > contentSize.width ? targetRect.size.width  - contentInset.left - contentInset.right : contentSize.width
            targetRect.size.height = targetRect.size.height - contentInset.top - contentInset.bottom > contentSize.height ? targetRect.size.height  - contentInset.top - contentInset.bottom : contentSize.height
        }
        return targetRect
    }
}