How to let a CAKeyframeAnimation pick up the current state when overriding another?

Question

I have one like this:

CALayer *layer = stripeButton.layer;
CAKeyframeAnimation *moveAnim = [CAKeyframeAnimation animationWithKeyPath:@"bounds.origin.y"];
moveAnim.duration = 3.35;
moveAnim.repeatCount = 0;
moveAnim.autoreverses = NO;
moveAnim.removedOnCompletion = NO;
moveAnim.calculationMode = kCAAnimationLinear;
moveAnim.fillMode = kCAFillModeForwards;

// ... keys and values here ...

[theLayer addAnimation:moveAnim forKey:@"theAnimation"];

You see this animation goes 3.35 seconds. In the meantime, it can happen that at i.e. 2 seconds a new animation with the same key @"theAnimation" is kicked off, for different values.

Problem what's happening: New animation does not pick up the current visible state. It begins hard from scratch. The view jumps to start position in a ugly manner and from there, the new animation begins. For UIView there is an setAnimationsBeginFromCurrentState=YES, but I haven't found anything like that for CAKeyFrameAnimation. Any idea?

Answer 1

You want to query the layer for its presentation layer, which is its current interpolated state including any animations currently running.

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Excerpt from the CALayer Class Reference:

 -(id)presentationLayer

Returns a copy of the layer containing all properties as they were at the start of the current transaction, with any active animations applied.

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The relationship of the Layer Tree (your data), the Presentation Tree (current interpolation values of your data), and the Render Tree are explained here in the CA programming guide.

Core Animation Rendering Architecture