title: Is this code, for horizontal page curl in iPhone, valid?
body: <p>I was Googling for applying horizontal page curl in iPhone. I also tried <a href="https://stackoverflow.com/questions/1625375/iphone-curl-left-and-curl-right-transitions">this</a>, but it wasn't appropriate for me (To change orientation and work in different ori.). I tried to search the web more. Finally I got <a href="http://forums.macrumors.com/showthread.php?t=508042" rel="nofollow noreferrer">this link</a>. From where, I could understand the horizontal page curl.</p>
  <p>But when I went to code deeply, I found some confusing points:</p>
  <ol>
  <li><p><code>extern NSString *kCAFilterPageCurl; // From QuartzCore.framework</code><br>
  is it valid to use internal variable ? ( as it's mentioned - from QuartzCore )</p>
  </li>
  <li><p><code>CAFilter *previousFilter = [[CAFilter filterWithType:kCAFilterPageCurl] retain];</code></p>
  <p>Above statement is giving warning ( not error ) -&gt; no '+filterWithType:' method found. Might be using internal (apple's private) method.</p>
  </li>
  <li><p><code>[previousFilter setDefaults];</code></p>
  <p>Above statement is giving warning ( not error ) -&gt; no '-setDefaults:' method found. Might be using internal (apple's private) method.</p>
  </li>
  </ol>
  <p>Now my queries.</p>
  <ol>
  <li>I have above doubts in the project (that might be using Apple's private methods).</li>
  <li>Is this code safe for apple store approval ?</li>
  <li>If 2's answer is wrong, what should be done for horizontal page curl ?</li>
  </ol>
  <p>In short, I want a horizontal page curl, and need your suggestions for having the proper solution, which might not trouble me in future.</p>