Animate Custom UIView Property in Swift

Question

all!

I have created a circular progress view using CoreGraphics that looks and updates like so:

50% 75%

The class is a UIView

Answer 1

Whilst AntonTheDev provides a great answer, his solution does not allow you to animate the CircularProgressView in an animation block, so you cant do neat things like:

UIView.animate(withDuration: 2, delay: 0, options: .curveEaseInOut, 
animations: {
    circularProgress.progress = 0.76
}, completion: nil)

There's a similar question here with a up to date Swift 3 answer based on ideas from the accepted answer and this post. This is what the final solution looks like.

Swift 3 Solution