How to launch gradient animation on button tapped? - swift

Question

I'm creating an IOS application. I have 5 buttons in star shapes created with UIBezierPath. And I want fill them when I tapped specific star. For ex. if I tapped 3-rd star then gradient will fill 3 first stars etc.
I have already created view with 5 stars. In the draw view method I have added code for animating gradient and it works fine only when view is launched.
override func draw(_ rect: CGRect) {
let path = UIBezierPath()
UIColor.black.setStroke()
path.lineWidth = 2
let numberOfPoints = 5
var angle: CGFloat = CGFloat.pi / 2
let angleOfIncrement = CGFloat.pi*2/CGFloat(numberOfPoints)
let radius: CGFloat = rect.origin.x + rect.width/2
let offset = CGPoint(x: rect.origin.x + rect.width/2, y: rect.origin.y + rect.height/2)
let midleRadius = radius*0.45
var firstStar = true
for _ in 1...numberOfPoints {
let firstPoint = getPointLocation(angle: angle, radius: midleRadius, offset: offset)
let midlePoint = getPointLocation(angle: angle+angleOfIncrement/2, radius: radius, offset: offset)
let secondPoint = getPointLocation(angle: angle+angleOfIncrement, radius: midleRadius, offset: offset)
if firstStar {
firstStar = false
path.move(to: firstPoint)
path.addLine(to: midlePoint)
path.addLine(to: secondPoint)
}else {
path.addLine(to: firstPoint)
path.addLine(to: midlePoint)
path.addLine(to: secondPoint)
}
angle += angleOfIncrement
}
path.stroke()
let shapeLayer = CAShapeLayer()
shapeLayer.path = path.cgPath
let gradient = CAGradientLayer(layer: layer)
gradient.colors = [UIColor.black.cgColor, UIColor.white.cgColor]
gradient.locations = [1]
gradient.startPoint = CGPoint(x: 0, y: 1)
gradient.endPoint = CGPoint(x: 1, y: 1)
gradient.frame = path.bounds
self.layer.addSublayer(gradient)
let animation = CABasicAnimation(keyPath: "locations")
animation.fromValue = [0, 0]
animation.toValue = [0, 1.0]
animation.duration = 3
gradient.add(animation, forKey: nil)
self.layer.mask = shapeLayer
}
I expect that when I tapped 3-rd star then gradient will fill first 3 stars.

Answer 1

You have to separate your drawing code from your animation code, and (btw.) you should also (re-)move the layer creation out of draw().
For the separation move
let animation = CABasicAnimation(keyPath: "locations")
animation.fromValue = [0, 0]
animation.toValue = [0, 1.0]
animation.duration = 3
gradient.add(animation, forKey: nil)
into a separate method and call it when needed.
You must also remove the layer creation from draw()because this method is always called if the view needs to be (re-)drawn. This produce a serious memory leak, because for instance every rotation of your iPhone will create a new gradient layer.
You have another issue in your code. Your gradient layer lies over the layer of the view. That cannot work. You may make the gradient layer to the view's layer, and work with mask, to cut the stars out of the gradient.