Why isn't my UIGraphicsImageRenderer drawing (iOS 10)?

Question

UIGraphicsImageRenderer is the new iOS 10 way to create an image context and draw into it. I'm trying to use UIGraphicsImageRenderer to draw a simple image:

let size = CGSize(width:100,height:100)
let f = UIGraphicsImageRendererFormat()
f.opaque = false
let r = UIGraphicsImageRenderer(size:size, format: f)
let im = r.image { _ in
    let p = UIBezierPath(ovalIn: CGRect(origin: CGPoint.zero, size: size))
    UIColor.blue().setFill()
    p.fill()
}
let iv = UIImageView(image:im)
iv.frame.origin = CGPoint(x: 200, y: 200)
self.view.addSubview(iv)

I expect to see a blue filled circle. But I don't see anything. What am I doing wrong?

PS I'm using Xcode 8 Seed 3, if it matters.

Answer 1

The problem is that that's not how you make a UIGraphicsImageRendererFormat. The documentation is a bit unclear on this point, but in fact you should be saying this:

let size = CGSize(width:100,height:100)
let f = UIGraphicsImageRendererFormat.default() // *
f.opaque = false
let r = UIGraphicsImageRenderer(size:size, format: f)
let im = r.image { _ in
    let p = UIBezierPath(ovalIn: CGRect(origin: CGPoint.zero, size: size))
    UIColor.blue().setFill()
    p.fill()
}
let iv = UIImageView(image:im)
iv.frame.origin = CGPoint(x: 200, y: 200)
self.view.addSubview(iv)

Your code will then work perfectly.

The problem with the previous code is that UIGraphicsImageRendererFormat() creates a completely unconfigured UIGraphicsImageRendererFormat, which is thus pretty much useless (unless you set all of its properties yourself).