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

Here's how I did it for an app I'm working on. The effect I was going for was bouncing when you pressed the view. Experiment with the values to suit your taste and the desired speed of the effect.

- (void) bounceView:(UIView*)bouncer
{
    // set duration to whatever you want
    float duration = 1.25;
    // use a consistent frame rate for smooth animation.
    // experiment to your taste
    float numSteps = 15 * duration;

    // scale the image up and down, halving the distance each time
    [UIView animateKeyframesWithDuration:duration
                                   delay:0
                                 options:UIViewKeyframeAnimationOptionCalculationModeCubic
                              animations:^{
                                  float minScale = 0.50f; // minimum amount of shrink
                                  float maxScale = 1.75f; // maximum amount of grow
                                  for(int i = 0; i< numSteps*2; i+=2)
                                  {
                                      // bounce down
                                      [UIView addKeyframeWithRelativeStartTime:duration/numSteps * i
                                                              relativeDuration:duration/numSteps
                                                                    animations:^{
                                                                        bouncer.layer.transform = CATransform3DMakeScale(minScale, minScale, 1);
                                                                    }];
                                      // bounce up
                                      [UIView addKeyframeWithRelativeStartTime:duration/numSteps * (i+1)
                                                              relativeDuration:duration/numSteps
                                                                    animations:^{
                                                                        bouncer.layer.transform = CATransform3DMakeScale(maxScale, maxScale, 1);
                                                                    }];

                                      // cut min scale halfway to identity
                                      minScale = minScale + (1.0f - minScale) / 2.0f;
                                      // cut max scale halfway to identity
                                      maxScale = 1.0f + (maxScale - 1.0f) / 2.0f;
                                  }
                              } completion:^(BOOL finished) {
                                  // quickly smooth out any rounding errors
                                  [UIView animateWithDuration:0.5*duration/numSteps animations:^{
                                      bouncer.layer.transform = CATransform3DIdentity;
                                  }];
                              }];
}