title: CGBitmapContextGetData result difference between iOS 3.2 and iOS 4.2
body: <p>I am having problem with iOS 3.2, the same code works fine on iOS 4.2, but with the 3.2, 
  CGBitmapContextGetData return nil</p>
  
  <p>my code:</p>
  
  <pre><code>CGContextRef context = CGBitmapContextCreate(
                                                   NULL,
                                                   image.size.width,
                                                   image.size.height,
                                                   8,
                                                   image.size.width * 4,
                                                   CGImageGetColorSpace(image.CGImage),
                                                   kCGImageAlphaPremultipliedLast
                                                   );
  
      if (context != NULL))   {
  
          CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage);
  
          UInt32 *contextData = CGBitmapContextGetData( context );
  }
  </code></pre>
  
  <p>contextData is nil when running on iOS 3.2, and returns the right value when running on iOS 4.2</p>
  
  <p>Any one can explain why the result is different, and how to solve it?</p>
  
  <p>Thanks.</p>