Create a universal vector image programmatically - ios

Question

We can now create universal vector images in Xcode by adding them into image assets folder and then changing the scale factors to single vector. I would like to know how to do this programmatically. I've tried the following but no luck :(
func resizeImage(image: UIImage, newSize: CGSize) -> (UIImage) {
let newRect = CGRectIntegral(CGRectMake(0,0, newSize.width, newSize.height))
let imageRef = image.CGImage
let scaleFactor = UIScreen.mainScreen().scale
UIGraphicsBeginImageContextWithOptions(newSize, false, scaleFactor)
// UIGraphicsBeginImageContextWithOptions(newSize, false, 0.5)
let context = UIGraphicsGetCurrentContext()
// Set the quality level to use when rescaling
CGContextSetInterpolationQuality(context, CGInterpolationQuality.High)
let flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, newSize.height)
CGContextConcatCTM(context, flipVertical)
// Draw into the context; this scales the image
CGContextDrawImage(context, newRect, imageRef)
let newImageRef = CGBitmapContextCreateImage(context)! as CGImage
let newImage = UIImage(CGImage: newImageRef)
// Get the resized image from the context and a UIImage
UIGraphicsEndImageContext()
return newImage
}

Answer 1

This should do it. Yea...Apple kind of gears this towards setting it in storyboard by ticking the preserve vector data. I'm not sure how to preserve vector data programmatically.
public class var add: UIImage {
let path = bundle.url(forResource: "plusReal", withExtension: "pdf")
return drawPDFFromURL(url: path!)!
}
class func drawPDFFromURL(url: URL) -> UIImage? {
guard let document = CGPDFDocument(url as CFURL),
let page = document.page(at: 1) else {return nil }
let pageRect = page.getBoxRect(.mediaBox)
let renderer = UIGraphicsImageRenderer(size: pageRect.size)
let img = renderer.image { ctx in
UIColor.white.set()
ctx.fill(pageRect)
ctx.cgContext.translateBy(x: 0.0, y: pageRect.size.height)
ctx.cgContext.scaleBy(x: 1.0, y: -1.0)
ctx.cgContext.drawPDFPage(page)
}
return img
}