Shaky Layer

gistfile1.m

#define degreesToRadian(x) (M_PI * (x) / 180.0)
+ (void)shakyWithLayer:(CALayer *)layer delegate:(id)object forKey:(NSString *)key {
    CAKeyframeAnimation * animation;
    animation = [CAKeyframeAnimation animationWithKeyPath:@"transform.rotation.z"];
    animation.duration = 0.25;
    animation.cumulative = YES;
    animation.repeatCount = 9999;
    animation.values = [NSArray arrayWithObjects:
                        [NSNumber numberWithFloat: 0.0], 
                        [NSNumber numberWithFloat: degreesToRadian(-4.0)], 
                        [NSNumber numberWithFloat: 0.0],
                        [NSNumber numberWithFloat: degreesToRadian(4.0)],
                        [NSNumber numberWithFloat: 0.0], nil];
    animation.fillMode = kCAFillModeForwards;
    animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    animation.removedOnCompletion = NO;
    animation.delegate = object;
    
    [layer addAnimation:animation forKey:key];
}