How to not use isRemovedOnCompletion for CAAnimation in iOS

Issue #228

CAAnimation is about presentation layer, after animation completes, the view snaps back to its original state. If we want to keep the state after animation, then the wrong way is to use CAMediaTimingFillMode.forward and isRemovedOnCompletion

Animation never ends

forwards https://developer.apple.com/documentation/quartzcore/camediatimingfillmode/1427658-forwards

The receiver remains visible in its final state when the animation is completed.

isRemovedOnCompletion

https://developer.apple.com/documentation/quartzcore/caanimation/1412458-isremovedoncompletion

When true, the animation is removed from the target layer’s animations once its active duration has passed. Defaults to true.

layer.fillMode = .forwards
animation. isRemovedOnCompletion = false

This is to tell the animation to never ends and keep its last presentation state. Wrong approach ❗️

Set final state before calling animation

The presentation state is just for animation, the source of truth lies in the layer itself. We need to set the final state before calling animation

let animation = CABasicAnimation(keyPath: #keyPath(CAShapeLayer.strokeEnd))

shapeLayer.strokeEnd = 1.0
shapeLayer.add(animation, forKey: "")