equivalent way drawing method to UIGraphicsGetCurrentContext - ios

Question

I have a swift class that outputs pie chart, I want to take out drawing logic out of drawRect method, since UIGraphicsGetCurrentContext returns nil outside of the draw method I need to change way of drawing my pie chart view,
What is the appropriate way to do this? My PieChart class looks like;
override func draw(_ rect: CGRect) {
let context: CGContext = UIGraphicsGetCurrentContext()!
drawLinearGradient(context)
drawCenterCircle(context)
let circle: CAShapeLayer = drawStroke()
let pathAnimation = CABasicAnimation(keyPath: "strokeEnd")
pathAnimation.duration = percentage
pathAnimation.toValue = percentage
pathAnimation.isRemovedOnCompletion = rendered ? false : (percentageLabel > 20 ? false : true)
pathAnimation.isAdditive = true
pathAnimation.fillMode = kCAFillModeForwards
circle.add(pathAnimation, forKey: "strokeEnd")
}
private func drawLinearGradient(_ context: CGContext) {
let circlePoint: CGRect = CGRect(x: 0, y: 0,
width: bounds.size.width, height: bounds.size.height)
context.addEllipse(in: circlePoint)
context.clip()
let colorSpace: CGColorSpace = CGColorSpaceCreateDeviceRGB()
let colorArray = [colors.0.cgColor, colors.1.cgColor]
let colorLocations: [CGFloat] = [0.0, 1.0]
let gradient = CGGradient(colorsSpace: colorSpace, colors: colorArray as CFArray, locations: colorLocations)
let startPoint = CGPoint.zero
let endPoint = CGPoint(x: 0, y: self.bounds.height)
context.drawLinearGradient(gradient!,
start: startPoint,
end: endPoint,
options: CGGradientDrawingOptions.drawsAfterEndLocation)
}
private func drawCenterCircle(_ context: CGContext) {
let circlePoint: CGRect = CGRect(x: arcWidth, y: arcWidth,
width: bounds.size.width-arcWidth*2,
height: bounds.size.height-arcWidth*2)
context.addEllipse(in: circlePoint)
UIColor.white.setFill()
context.fillPath()
}
private func drawStroke() -> CAShapeLayer {
let circle = CAShapeLayer()
self.layer.addSublayer(circle)
return circle
}

Answer 1

You can change your code to produce a UIImage containing the pie chart, and then place that image inside an image view:
UIGraphicsBeginImageContext(size)
let context = UIGraphicsGetCurrentContext()
// ... here goes your drawing code, just as before
let pieImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
let pieView = UIImageView(image: pieImage)
Note that if you need to update the chart very frequently (multiple times per second), this solution might bring a performance penalty because the image creation takes a bit more time then the pure rendering.