Fill circle border with gradient color using UIBezierPath

Question

I want to fill half of a circle's border using UIBazierpath with gradient color.

Initially I tried with the full circle but it's not working, the gradient always fills the circle but not the border. Is there any way to do this?

Here's what I have so far:

let path = UIBezierPath(roundedRect: rect, cornerRadius: rect.width/2)
let shape = CAShapeLayer()
shape.path = path.cgPath
shape.lineWidth = 2.0
shape.strokeColor = UIColor.black.cgColor
self.layer.addSublayer(shape)

let gradient = CAGradientLayer()
gradient.frame = path.bounds
gradient.colors = [UIColor.magenta.cgColor, UIColor.cyan.cgColor]

let shapeMask = CAShapeLayer()
shapeMask.path = path.cgPath
gradient.mask = shapeMask
shapeMask.lineWidth = 2

self.layer.addSublayer(gradient)

Edit: Added the image. I want to achieve something like this.

Answer 1

Core graphics doesn't support an axial gradient so you need to draw this out in a more manual way.

Here's a custom view class that draws a circle using the range of HSV colors around the circumference.

class RadialCircleView: UIView {
    override func draw(_ rect: CGRect) {
        let thickness: CGFloat = 20
        let center = CGPoint(x: bounds.midX, y: bounds.midY)
        let radius = min(bounds.width, bounds.height) / 2 - thickness / 2
        var last: CGFloat = 0
        for a in 1...360 {
            let ang = CGFloat(a) / 180 * .pi
            let arc = UIBezierPath(arcCenter: center, radius: radius, startAngle: last, endAngle: ang, clockwise: true)
            arc.lineWidth = thickness
            last = ang
            UIColor(hue: CGFloat(a) / 360, saturation: 1, brightness: 1, alpha: 1).set()
            arc.stroke()
        }
    }
}

let radial = RadialCircleView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
radial.backgroundColor = UIColor(red: 0.98, green: 0.92, blue: 0.84, alpha: 1) // "antique white"

Copy this into a playground to experiment with the results. The colors don't exactly match your image but it may meet your needs.