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

In iOS 7.0 or later, UIKit keyframe animation is available.

[UIView animateKeyframesWithDuration:0.5 delay:0.0 options:0 animations:^{
    [UIView setAnimationCurve:UIViewAnimationCurveLinear];

    NSInteger repeatCount = 8;
    NSTimeInterval duration = 1.0 / (NSTimeInterval)repeatCount;

    for (NSInteger i = 0; i < repeatCount; i++) {
        [UIView addKeyframeWithRelativeStartTime:i * duration relativeDuration:duration animations:^{
            CGFloat dx = 5.0;
            if (i == repeatCount - 1) {
                viewToShake.transform = CGAffineTransformIdentity;
            } else if (i % 2) {
                viewToShake.transform = CGAffineTransformTranslate(CGAffineTransformIdentity, -dx, 0.0);
            } else {
                viewToShake.transform = CGAffineTransformTranslate(CGAffineTransformIdentity, +dx, 0.0);
            }
        }];
    }
} completion:completion];