core animation - 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.

So I'd like for it to graphically shake my login view when the user enters the wrong user ID and password like the Mac login screen does.

Anyone know if there's a way to pull this off, or have any suggestions for another effect I could use?

Answer 1

I think this is a more efficient solution:

Swift:

let anim = CAKeyframeAnimation( keyPath:"transform" )
anim.values = [
    NSValue( CATransform3D:CATransform3DMakeTranslation(-5, 0, 0 ) ),
    NSValue( CATransform3D:CATransform3DMakeTranslation( 5, 0, 0 ) )
]
anim.autoreverses = true
anim.repeatCount = 2
anim.duration = 7/100

viewToShake.layer.addAnimation( anim, forKey:nil )

Obj-C:

CAKeyframeAnimation * anim = [ CAKeyframeAnimation animationWithKeyPath:@"transform" ] ;
anim.values = @[ 
    [ NSValue valueWithCATransform3D:CATransform3DMakeTranslation(-5.0f, 0.0f, 0.0f) ], 
    [ NSValue valueWithCATransform3D:CATransform3DMakeTranslation( 5.0f, 0.0f, 0.0f) ] 
] ;
anim.autoreverses = YES ;
anim.repeatCount = 2.0f ;
anim.duration = 0.07f ;

[ viewToShake.layer addAnimation:anim forKey:nil ] ;

Only one animation object is created and it's all performed at the CoreAnimation level.