title: How to animate when switching CALayers
body: <p>I'm adding and removing <code>CALayers</code> using this method : </p>
  
  <pre><code>[[[self.view.layer sublayers] objectAtIndex:0] removeFromSuperlayer];
      if(++self.backgroundIndex &gt; self.gradients.count - 1) {
          self.backgroundIndex = 0;
      }
      CAGradientLayer *layer = [self.gradients objectAtIndex:self.backgroundIndex];
      layer.frame = self.view.frame;
      [self.view.layer insertSublayer:layer atIndex:0];
  </code></pre>
  
  <p>How can I animate this ? Thanks.</p>