rotate a UIView around its center but several time

问题:

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 = CGAffineTransformMakeRotation(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 animatationBlock. 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

回答1:

You can use the following animation on 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"];

回答2:

As Brad Larson indicated, you can do this with a CAKeyframeAnimation. For instance,

CAKeyframeAnimation *rotationAnimation;
rotationAnimation = 
   [CAKeyframeAnimation animationWithKeyPath:@"transform.rotation.z"];

rotationAnimation.values = [NSArray arrayWithObjects:
                            [NSNumber numberWithFloat:0.0 * M_PI], 
                            [NSNumber numberWithFloat:0.75 * M_PI], 
                            [NSNumber numberWithFloat:1.5 * M_PI], 
                            [NSNumber numberWithFloat:2.0 * M_PI], nil]; 
rotationAnimation.calculationMode = kCAAnimationPaced;
rotationAnimation.removedOnCompletion = NO;
rotationAnimation.fillMode = kCAFillModeForwards;
rotationAnimation.timingFunction = 
   [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
rotationAnimation.duration = 10.0;

CALayer *layer = [viewToSpin layer];
[layer addAnimation:rotationAnimation forKey:@"rotationAnimation"];

You can control the duration of the total animation with the rotationAnimation.duration property, and the acceleration and deceleration (and calculation of steps in between) with the rotationAnimation.timingFunction property.

回答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.

回答4:

CABasicAnimation* animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
animation.fromValue = [NSNumber numberWithFloat:0.0f];
animation.toValue = [NSNumber numberWithFloat: 2*M_PI];
animation.duration = 8.0f;
animation.repeatCount = INFINITY;
[self.myView.layer addAnimation:animation forKey:@"SpinAnimation"];