title: executing code (selector) while animating CABasicAnimation
body: <pre><code>CABasicAnimation *rotationAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.y"];
  rotationAnimation.toValue = [NSNumber numberWithFloat: 2*M_PI];
  rotationAnimation.duration = 1.0;
  [self.layer addAnimation:rotationAnimation forKey:@"rotationAnimation1"];
  </code></pre>
  
  <p>I would like to execute code when the degree is M_PI, in other words I have two buttons on the UIView and I want to change the labels of them while rotating the UIView and I don't want the user to feel the the buttons are changing in front of him so , best way is to execute the label changing while the UIView is rotating to half of the way.</p>
  
  <p>Help me</p>