Shake visual effect on iPhone (NOT shaking the device)

Question

On login failure, I\'d prefer to avoid showing an alert, it\'s too fleeting. Showing the alert and then showing the text somewhere on the login screen seems like duplication

Answer 1

I know the question is already answered, but since I have already implemented something like this previously, I feel it can't hurt to add it:

CAKeyframeAnimation *shakeAnimation = [CAKeyframeAnimation animationWithKeyPath:@"transform.rotation.z"];
NSArray *transformValues = [NSArray arrayWithObjects:
                        [NSNumber numberWithFloat:((M_PI)/64)],
                        [NSNumber numberWithFloat:(-((M_PI)/64))],
                        [NSNumber numberWithFloat:((M_PI)/64)],
                        [NSNumber numberWithFloat:(-((M_PI)/64))],
                        [NSNumber numberWithFloat:((M_PI)/64)],
                        [NSNumber numberWithFloat:(-((M_PI)/64))],
                        [NSNumber numberWithFloat:0],                                
                        nil];

[shakeAnimation setValues:transformValues];

NSArray *times = [NSArray arrayWithObjects:
                  [NSNumber numberWithFloat:0.14f],
                  [NSNumber numberWithFloat:0.28f],
                  [NSNumber numberWithFloat:0.42f],
                  [NSNumber numberWithFloat:0.57f],
                  [NSNumber numberWithFloat:0.71f],
                  [NSNumber numberWithFloat:0.85f],
                  [NSNumber numberWithFloat:1.0f], 
                  nil];

[shakeAnimation setKeyTimes:times];

shakeAnimation.fillMode = kCAFillModeForwards;
shakeAnimation.removedOnCompletion = NO;
shakeAnimation.duration = 0.6f;

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

Also, since you want the shaking to indicate that the user failed to log in, you might also consider adding this animation that tints the screen red while the screen shakes:

//Put this in the header (.h)
@property (nonatomic, strong) UIView *redView;

//Put this in the implementation (.m)
@synthesize redView;

//Put this in viewDidLoad
self.redView = [[UIView alloc] initWithFrame:self.view.frame];
self.redView.layer.opacity = 0.0f;
self.redView.layer.backgroundColor = [[UIColor redColor] CGColor];

//Put this wherever you check if the login failed
CAKeyframeAnimation *redTint = [CAKeyframeAnimation animationWithKeyPath:@"opacity"];
NSArray *transformValues = [NSArray arrayWithObjects:
                           [NSNumber numberWithFloat:0.2f],
                           [NSNumber numberWithFloat:0.0f],                                
                           nil];

[redTint setValues:transformValues];

NSArray *times = [NSArray arrayWithObjects:
                  [NSNumber numberWithFloat:0.5f],
                  [NSNumber numberWithFloat:1.0f], 
                  nil];

[redTint setKeyTimes:times];

redTint.fillMode = kCAFillModeForwards;
redTint.removedOnCompletion = NO;
redTint.duration = 0.6f;

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

Hope this helps!