CABasicAnimation reverse(backwards) - swift

Question

I'm a bit struggling with this simple line animation. I figured out how to pause it, but what I need is to be able to reverse animation back to starting point from the moment I call function resetAnimation().
let pathAnimation = CABasicAnimation(keyPath: "strokeEnd")
let pathLayer = CAShapeLayer()
func lineAnimation() {
let path = UIBezierPath()
let screenWidth = self.view.bounds.width
let screenHeight = self.view.bounds.height
path.moveToPoint(CGPointMake(screenWidth, screenHeight / 2))
path.addLineToPoint(CGPointMake(screenWidth - screenWidth, screenHeight / 2))
self.pathLayer.frame = self.view.bounds
self.pathLayer.path = path.CGPath
self.pathLayer.strokeColor = UIColor.whiteColor().CGColor
self.pathLayer.fillColor = nil
self.pathLayer.lineWidth = 3.0
self.pathLayer.lineCap = kCALineCapRound
self.pathLayer.speed = 1
self.view.layer.addSublayer(pathLayer)
self.pathAnimation.duration = 5.0
self.pathAnimation.fromValue = 0.0
self.pathAnimation.toValue = 1.0
pathLayer.addAnimation(pathAnimation, forKey: "animate")
}
func pauseAnimation() {
let pausedTime = pathLayer.convertTime(CACurrentMediaTime(), fromLayer: nil)
pathLayer.speed = 0
pathLayer.timeOffset = pausedTime
}
func resetAnimation() {
}

Answer 1

You just need to create a new animation and remove the old one. Your starting point for the new animation will be the current value of that property in your presentation layer. I'd also recommend setting the frame of your shape layer to the bounds of the actual bezier shape instead of the entire view - its a good habit to be in when you start moving things around and scaling/rotating/etc. Otherwise you're gonna be faced with a bunch of funky conversions or anchor point changes.
Here's what I'd do:
let pathLayer = CAShapeLayer()
// first, separate your drawing code from your animation code.
// this way you can call animations without instantiating new objects
func drawLine() {
let path = UIBezierPath()
// draw your path with no position translation.. move the layer
path.moveToPoint(CGPointMake(view.bounds.width, 0))
path.addLineToPoint(CGPointMake(0, 0))
pathLayer.frame = path.bounds
// this line sets the position of the layer appropriately
pathLayer.position = view.bounds.width - pathLayer.bounds.width / 2
pathLayer.path = path.CGPath
pathLayer.strokeColor = UIColor.whiteColor().CGColor
pathLayer.fillColor = nil
pathLayer.lineWidth = 3.0
pathLayer.lineCap = kCALineCapRound
view.layer.addSublayer(pathLayer)
}
func lineAnimation() {
let pathAnimation = CABasicAnimation(keyPath: "strokeEnd")
pathAnimation.duration = 5.0
pathAnimation.fromValue = 0.0
pathAnimation.toValue = 1.0
pathLayer.addAnimation(pathAnimation, forKey: "strokeEnd")
}
func reverseAnimation() {
let revAnimation = CABasicAnimation(keyPath: "strokeEnd")
revAnimation.duration = 5.0
// every Core Animation has a 'presentation layer' that contains the animated changes
revAnimation.fromValue = pathLayer.presentationLayer()?.strokeEnd
revAnimation.toValue = 0.0
pathLayer.removeAllAnimations()
pathLayer.addAnimation(revAnimation, forKey: "strokeEnd")
}
Keep in mind you'll also want to set your properties so you retain the end values of the animation.

Answer 2

You could also use the autoreverses property of CAMediaTiming protocol, which is complied by CABasicAnimation