'Press and hold' animation without NSTimer - ios

Question

Update: The NSTimer approach works now, but comes with a huge performance hit. The question is now narrowed down to an approach without NSTimers.
I'm trying to animate a 'Press and hold' interactive animation. After following a load of SO answers, I've mostly followed the approach in Controlling Animation Timing by #david-rönnqvist. And it works, if I use a Slider to pass the layer.timeOffset.
However, I can't seem to find a good way to continuously update the same animation on a press and hold gesture. The animation either doesn't start, only shows the beginning frame or at some points finishes and refuses to start again.
Can anyone help with achieving the following effect, without the horrible NSTimer approach I'm currently experimenting with?
On user press, animation starts, circle fills up.
While user holds (not necessarily moving the finger), the animation should continue until the end and stay on that frame.
When user lifts finger, the animation should reverse, so the circle is empties again.
If the user lifts his finger during the animation or presses down again during the reverse, the animation should respond accordingly and either fill or empty from the current frame.
Here's a Github repo with my current efforts.
As mentioned, the following code works well. It's triggered by a slider and does its job great.
func animationTimeOffsetToPercentage(percentage: Double) {
if fillShapeLayer == nil {
fillShapeLayer = constructFillShapeLayer()
}
guard let fillAnimationLayer = fillShapeLayer, let _ = fillAnimationLayer.animationForKey("animation") else {
print("Animation not found")
return
}
let timeOffset = maximumDuration * percentage
print("Set animation to percentage \(percentage) with timeOffset: \(timeOffset)")
fillAnimationLayer.timeOffset = timeOffset
}
However, the following approach with NSTimers works, but has an incredible performance hit. I'm looking for an approach which doesn't use the NSTimer.
func beginAnimation() {
if fillShapeLayer == nil {
fillShapeLayer = constructFillShapeLayer()
}
animationTimer?.invalidate()
animationTimer = NSTimer.schedule(interval: 0.1, repeats: true, block: { [unowned self] () -> Void in
if self.layer.timeOffset >= 1.0 {
self.layer.timeOffset = self.maximumDuration
}
else {
self.layer.timeOffset += 0.1
}
})
}
func reverseAnimation() {
guard let fillAnimationLayer = fillShapeLayer, let _ = fillAnimationLayer.animationForKey("animation") else {
print("Animation not found")
return
}
animationTimer?.invalidate()
animationTimer = NSTimer.schedule(interval: 0.1, repeats: true, block: { [unowned self] () -> Void in
if self.layer.timeOffset <= 0.0 {
self.layer.timeOffset = 0.0
}
else {
self.layer.timeOffset -= 0.1
}
})
}

Answer 1

When you use slider you use fillAnimationLayer layer for animation
fillAnimationLayer.timeOffset = timeOffset
However, in beginAnimation and reverseAnimation functions you are using self.layer.
Try to replace self.layer.timeOffset with self.fillShapeLayer!.timeOffset in your timer blocks.

Answer 2

The solution is two-fold;
Make sure the animation doesn't remove itself on completion and keeps its final frame. Easily accomplished with the following lines of code;
animation.fillMode = kCAFillModeForwards
animation.removedOnCompletion = false
The hard part; you have to remove the original animation and start a new, fresh reverse animation that begins at the correct point. Doing this, gives me the following code;
func setAnimation(layer: CAShapeLayer, startPath: AnyObject, endPath: AnyObject, duration: Double)
{
// Always create a new animation.
let animation: CABasicAnimation = CABasicAnimation(keyPath: "path")
if let currentAnimation = layer.animationForKey("animation") as? CABasicAnimation {
// If an animation exists, reverse it.
animation.fromValue = currentAnimation.toValue
animation.toValue = currentAnimation.fromValue
let pauseTime = layer.convertTime(CACurrentMediaTime(), fromLayer: nil)
// For the timeSinceStart, we take the minimum from the duration or the time passed.
// If not, holding the animation longer than its duration would cause a delay in the reverse animation.
let timeSinceStart = min(pauseTime - startTime, currentAnimation.duration)
// Now convert for the reverse animation.
let reversePauseTime = currentAnimation.duration - timeSinceStart
animation.beginTime = pauseTime - reversePauseTime
// Remove the old animation
layer.removeAnimationForKey("animation")
// Reset startTime, to be when the reverse WOULD HAVE started.
startTime = animation.beginTime
}
else {
// This happens when there is no current animation happening.
startTime = layer.convertTime(CACurrentMediaTime(), fromLayer: nil)
animation.fromValue = startPath
animation.toValue = endPath
}
animation.duration = duration
animation.fillMode = kCAFillModeForwards
animation.removedOnCompletion = false
layer.addAnimation(animation, forKey: "animation")
}
This Apple article explains how to do a proper pause and resume animation, which is converted to use with the reverse animation.