CAKeyFrameAnimation presentation layer seems not to change

Question

I'm using CAKeyframeAnimation to move CALayer on a circle trajectory. Sometimes I need to stop animation and to move animation to the point at which the animation stopped. Here the code:

CAKeyframeAnimation* circlePathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
CGMutablePathRef circularPath = the circle path;

circlePathAnimation.path = circularPath;
circlePathAnimation.delegate = self;
circlePathAnimation.duration = 3.0f;
circlePathAnimation.repeatCount = 1;
circlePathAnimation.fillMode = kCAFillModeForwards;
circlePathAnimation.removedOnCompletion = NO;
circlePathAnimation.timingFunction = [CAMediaTimingFunction functionWithControlPoints:.43 :.78 :.69 :.99];
[circlePathAnimation setValue:layer forKey:@"animationLayer"];
[layer addAnimation:circlePathAnimation forKey:@"Rotation"];


- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag
{
    CALayer *layer = [anim valueForKey:@"animationLayer"];
    if (layer) {
        CALayer *presentationLayer = layer.presentationLayer;
        layer.position = presentationLayer.position;
    }
}

But the presentation layer has no changes in position!!! I read that it is no longer reliable from ios 8. So is there any other way I can find the current position of animated layer?

I've gotten the position (actually, frame.origin) of animating objects using the presentation layer in iOS 8, and it seemed to work fine. Can you provide a reference to where you read that it's no longer reliable? I tested it with presentationLayer.position, and that worked too. — rdelmar, Apr 05 '15 at 00:24

score 1 · Accepted Answer · answered Apr 04 '15 at 22:21

I wasn't aware that the position property of the presentation layer stopped telling you the location of your layer in iOS 8. That's interesting. Hit testing using the hitTest method on the presentation layer still works, I just tried it on an app I wrote a while back.

Pausing and resuming an animation also still works.

For a simple path like a circle path you could check the time of the animation and then calculate the position using trig.

For more complex paths you'd have to know about the path your layer was traversing. Plotting a single cubic or quadratic bezier curve over time is pretty straightforward, but a complex UIBezierPath/CGPath with a mixture of different shapes in it would be a bear to figure out.

CAKeyFrameAnimation presentation layer seems not to change

1 Answers1