Mimic UIAlertView Bounce?

Question

Whats the best way to mimic the bouncing animation from the UIAlertView on the iPhone? Is there some built-in mechanism for this? The UIAlertView itself won\'t work for my n

Answer 1

I investigated how animations are added to UIAlertView's layer by swizzling -[CALayer addAnimation:forKey:]. Here are the values I got for the scale transform animations it performs:

0.01f -> 1.10f -> 0.90f -> 1.00f

with durations

0.2s, 0.1s, 0.1s.

All the animations use an ease in/ease out timing function. Here is a CAKeyframeAnimation that encapsulates this logic:

CAKeyframeAnimation *bounceAnimation = [CAKeyframeAnimation animationWithKeyPath:@"transform"];
bounceAnimation.fillMode = kCAFillModeBoth;
bounceAnimation.removedOnCompletion = YES;
bounceAnimation.duration = 0.4;
bounceAnimation.values = @[
    [NSValue valueWithCATransform3D:CATransform3DMakeScale(0.01f, 0.01f, 0.01f)],
    [NSValue valueWithCATransform3D:CATransform3DMakeScale(1.1f, 1.1f, 1.1f)],
    [NSValue valueWithCATransform3D:CATransform3DMakeScale(0.9f, 0.9f, 0.9f)],
    [NSValue valueWithCATransform3D:CATransform3DIdentity]];
bounceAnimation.keyTimes = @[@0.0f, @0.5f, @0.75f, @1.0f];
bounceAnimation.timingFunctions = @[
    [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut],
    [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut],
    [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut]];

I believe UIAlertView also performs a simple opacity animation from 0.0f to 1.0f over the total duration of the transform animation (0.4).