title: About layer.shadow on iOS development
body: <p>if I use layer.shadow like this:</p>
  
  <pre><code>self.layer.shadowOffset = CGSizeMake(0, 1.5);
  self.layer.shadowColor = [UIColor grayColor].CGColor;
  self.layer.shadowOpacity = 1;
  </code></pre>
  
  <p>and put some(not more than 10) of these views(without images) into a <code>UIScrollView</code>,
  it makes the <code>scrollView</code> very slow when is scrolling.</p>
  
  <p>if I remove any codes about shadow, scrolling become quite smooth again.</p>
  
  <p>FYI, the un-smooth case happen when running the app on iOS device,
  but smooth on iOS simulator.</p>
  
  <p>Does any one know how to keep both shadow and smooth scrolling? </p>