CAKeyframeAnimation Keypath Error

Question

I am trying to animate the transform property of a view. Here is my code:

CAKeyframeAnimation *shakeAnimation = [CAKeyframeAnimation animationWithKeyPath:@"transform"];
NSArray *transformValues = [NSArray arrayWithObjects:
                        [NSValue valueWithCGAffineTransform:CGAffineTransformMakeRotation((3*M_PI)/8)],
                        [NSValue valueWithCGAffineTransform:CGAffineTransformMakeRotation(-((3*M_PI)/8))],
                        [NSValue valueWithCGAffineTransform:CGAffineTransformMakeRotation((3*M_PI)/8)],
                        [NSValue valueWithCGAffineTransform:CGAffineTransformMakeRotation(-((3*M_PI)/8))],
                        [NSValue valueWithCGAffineTransform:CGAffineTransformMakeRotation((3*M_PI)/8)],
                        [NSValue valueWithCGAffineTransform:CGAffineTransformMakeRotation(-((3*M_PI)/8))],
                        nil];

[shakeAnimation setValues:transformValues];

NSArray *times = [NSArray arrayWithObjects:[NSNumber numberWithFloat:0.16f],[NSNumber numberWithFloat:0.33f],[NSNumber numberWithFloat:0.49f],[NSNumber numberWithFloat:0.66f],[NSNumber numberWithFloat:0.82f], [NSNumber numberWithFloat:1.0f], nil];

[shakeAnimation setKeyTimes:times];

NSArray *timingFunctions = [NSArray arrayWithObjects:
[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut], 
[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut],
[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut], 
[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut], 
[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut], 
[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut], 
nil];

[shakeAnimation setTimingFunctions:timingFunctions];

shakeAnimation.fillMode = kCAFillModeForwards;
shakeAnimation.removedOnCompletion = NO;
shakeAnimation.duration = 1.0f;

[self.someView.layer addAnimation:shakeAnimation forKey:@"anim"];

For some reason, I get an error whenever I set the parameter of the method animationWithKeyPath: to "transform". I have tried for half an hour to debug this, but can't find the error. I initially though that I was performing an animation not allowed on a UIView's transform property, but I know that I can do something like this:

aView.transform = CGAffineTransformMakeRotation(M_PI/2);

Thanks in advanced.

Answer 1

The value of a layer's transform property is a CATransform3D, not a CGAffineTransform.

Also, you might find it simpler to animate the transform.rotation.z key path. The value is just a CGFloat, so you don't have to create a transform matrix at all.

“Modifying a Transform Using Key Paths” in Core Animation Programming Guide
“Key Path Support for Structure Fields” in Core Animation Programming Guide