rotate a UIView around its center but several times..

Question

I'm trying to rotate some UIView around its center, so the simple code goes something like (in pseudocode):

[UIView beginAnimations:@"crazyRotate" context:nil];
[UIView setAnimationDuration:1.0];
someview.transform = CGAffineTransformMakeRotate(angle);
[UIView commitAnimations]

now if I set angle to say M_PI/2 the thing rotates nicely. if I set it to 2*M_PI, well it does "nothing". I can understand that the matrix translates to something that does nothing (rotating 360 means "stay" in a sense), yet, I want to rotate it 5 times (think of a newspaper rotate scale coming at you effect -- I'm not great at describing..hope someone understands). So, I tried adding setting angle to 180 deg (M_PI) and add a nested animatation block. but I guess that since I'm setting the same property (someview.transition) again it ignores it somehow). I tried setting repeat count of the animation to 2 with angle M_PI but it seems to simply rotate 180, going back to straight position and then initiating the rotate again.

So, I'm a little out of ideas, any help appreciated! --t

Answer 1

You can use the following animation of your UIView's layer property. I've tested it.

UIView *viewToSpin = ...;    
CABasicAnimation* spinAnimation = [CABasicAnimation
                                  animationWithKeyPath:@"transform.rotation"];
spinAnimation.toValue = [NSNumber numberWithFloat:5*2*M_PI];
[viewToSpin.layer addAnimation:spinAnimation forKey:@"spinAnimation"];

Answer 2

Hey!

Thanks for the quick reply. This is a good solution in a sense, though 5.2*M_PI is not exactly a full spin per say. Pragmatically (are we ever though??) your solution solves the problem of course but I stil can't stop wondering why the nested animation block (each block doing a half turn) does not work. Do you have an idea?

thanx again! -t

Answer 3

Getting a continuous spinning effect is a little tricky, but I describe a means to do it here. Yes, Core Animation seems to optimize transforms to the closest ending position within the unit circle. The method I describe there chains a few half-rotation animations together to make full rotations, although you do notice a slight stutter in the handoff from one animation to the next.

Perhaps a CAKeyframeAnimation constructed with these half-rotation values would be the right way to go. Then you could also control acceleration and deceleration.

Answer 4

Hey Brad, Nice, but to be honest its again a workaround and hence the little (almost un-noticed jump between the animations), If anyone has even more in depth understanding of how stacking of animations on UIView works I would love to hear about it, Again, thanks for the tips and help, --tzurs