title: UIScrollView and CATiledLayer
body: <p>I am using a CATiledLayer as content of UIScrollView, but seems I can not get the correct (sometimes) [scrollView contentSize] and [scrollView contentOffset] from CATiledLayer's delegate method : </p>
  
  <pre><code>- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx
  </code></pre>
  
  <p>I know CATiledLayer uses this method to render tile in a background thread. And I need to use contentSize and contentOffset to calculate some data (some coordinates). The app ran fine on simulator but on device, it sometimes got the wrong contentSize and contentOffset</p>