rotation.m

- (void) startRotatingWithDuration: (double) duration {
    NSString *animKey = @"rotation";
    if([self.layer animationForKey: animKey] == nil) {
        CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath: @"transform.rotation"];
        animation.duration = duration;
        animation.repeatCount = INFINITY;
        /*animation.fromValue = [NSNumber numberWithFloat: 0.0];*/
        animation.toValue = [NSNumber numberWithFloat: 2*M_PI];
        [self.layer addAnimation: animation forKey: animKey];
    }
}

- (void) stopRotation {
    NSString *animKey = @"rotation";
    if([self.layer animationForKey: animKey] != nil) {
        [self.layer removeAnimationForKey: animKey];
    }
}