Animating a circular progress circle smoothly via buttons - ios

Question

I am experiencing odd visual quirks with my progress circle. I would like the green circle (CAShapeLayer) to smoothly animate in increments of fifths. 0/5 = no green circle. 5/5 = full green circle. The problem is the green circle is animating past where it should be, then abruptly shrinks back to the proper spot. This happens when both the plus and minus button are pressed. There is a gif below demonstrating what is happening.
The duration of each animation should last 0.25 seconds, and should smoothly animate both UP and DOWN (depending if the plus or minus button is pressed) from wherever the animation ended last (which is currently not happening.)
In my UIView, I draw the circle, along with the method to animate the position of the progress:
class CircleView: UIView {
let progressCircle = CAShapeLayer()
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override init(frame: CGRect) {
super.init(frame: frame)
}
override func draw(_ rect: CGRect) {
let circlePath = UIBezierPath(ovalIn: self.bounds)
progressCircle.path = circlePath.cgPath
progressCircle.strokeColor = UIColor.green.cgColor
progressCircle.fillColor = UIColor.red.cgColor
progressCircle.lineWidth = 10.0
// Add the circle to the view.
self.layer.addSublayer(progressCircle)
}
func animateCircle(circleToValue: CGFloat) {
let fifths:CGFloat = circleToValue / 5
let animation = CABasicAnimation(keyPath: "strokeEnd")
animation.duration = 0.25
animation.fromValue = fifths
animation.byValue = fifths
animation.fillMode = kCAFillModeBoth
animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
progressCircle.strokeEnd = fifths
// Create the animation.
progressCircle.add(animation, forKey: "strokeEnd")
}
}
In my VC:
I init the circle and starting point with:
let myDrawnCircle = CircleView()
var startingPointForCircle = CGFloat()
viewDidAppear:
startingPointForCircle = 0.0
myDrawnCircle.frame = CGRect(x: 100, y: 100, width: 150, height: 150)
myDrawnCircle.backgroundColor = UIColor.white
myDrawnCircle.animateCircle(circleToValue: startingPointForCircle)
self.view.addSubview(myDrawnCircle)
textLabel.text = "\(startingPointForCircle)"
And the actual buttons that do the cool animating:
#IBAction func minusButtonPressed(_ sender: UIButton) {
if startingPointForCircle > 0 {
startingPointForCircle -= 1
textLabel.text = "\(startingPointForCircle)"
myDrawnCircle.animateCircle(circleToValue: startingPointForCircle)
}
}
#IBAction func plusButtonPressed(_ sender: UIButton) {
if startingPointForCircle < 5 {
startingPointForCircle += 1
textLabel.text = "\(startingPointForCircle)"
myDrawnCircle.animateCircle(circleToValue: startingPointForCircle)
}
}
Here's a gif showing you what's going on with the jerky animations.
How do I make my animations smoothly animate TO the proper value FROM the proper value?

Answer 1

My guess is it has something to do with using a key path. I don't know how exactly to fix it for using a key path, but you could try a different tack, using a custom view, and animating the value passed to the method used for drawing an arc.
The code below was generated by PaintCode. The value passed for arc specifies the point on the circle to draw the arc to. This is used in the drawRect method of a custom UIView. Make a CGFloat property of the custom view and simply change that value, and call setNeedsDisplay on the view after your animation code.
func drawCircleProgress(frame frame: CGRect = CGRect(x: 0, y: 0, width: 40, height: 40), arc: CGFloat = 270) {
//// General Declarations
let context = UIGraphicsGetCurrentContext()
//// Color Declarations
let white = UIColor(red: 1.000, green: 1.000, blue: 1.000, alpha: 1.000)
let white50 = white.colorWithAlpha(0.5)
//// Oval Drawing
CGContextSaveGState(context)
CGContextTranslateCTM(context, frame.minX + 20, frame.minY + 20)
CGContextRotateCTM(context, -90 * CGFloat(M_PI) / 180)
let ovalRect = CGRect(x: -19.5, y: -19.5, width: 39, height: 39)
let ovalPath = UIBezierPath()
ovalPath.addArcWithCenter(CGPoint(x: ovalRect.midX, y: ovalRect.midY), radius: ovalRect.width / 2, startAngle: 0 * CGFloat(M_PI)/180, endAngle: -arc * CGFloat(M_PI)/180, clockwise: true)
white.setStroke()
ovalPath.lineWidth = 1
ovalPath.stroke()
CGContextRestoreGState(context)
}

Answer 2

The desired results were as simple as commenting out fromValue / byValue in the animateCircle method. This was pointed out by #dfri - "set both fromValue and toValue to nil then: "Interpolates between the previous value of keyPath in the target layer’s presentation layer and the current value of keyPath in the target layer’s presentation layer."
//animation.fromValue = fifths
//animation.byValue = fifths