Is this code, for horizontal page curl in iPhone, valid?

I was Googling for applying horizontal page curl in iPhone. I also tried this, 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 this link. From where, I could understand the horizontal page curl.

But when I went to code deeply, I found some confusing points:

1. extern NSString *kCAFilterPageCurl; // From QuartzCore.framework

   is it valid to use internal variable ? ( as it's mentioned - from QuartzCore )

2. CAFilter *previousFilter = [[CAFilter filterWithType:kCAFilterPageCurl] retain];

   Above statement is giving warning ( not error ) -> no '+filterWithType:' method found. Might be using internal (apple's private) method.

3. [previousFilter setDefaults];

   Above statement is giving warning ( not error ) -> no '-setDefaults:' method found. Might be using internal (apple's private) method.

Now my queries.

1. I have above doubts in the project (that might be using Apple's private methods).
2. Is this code safe for apple store approval ?
3. If 2's answer is wrong, what should be done for horizontal page curl ?

In short, I want a horizontal page curl, and need your suggestions for having the proper solution, which might not trouble me in fut开发者_如何学运维ure.

CAFilter is private API, that's why you see compiler errors and warnings. What's worse is that Apple may reject your application for use of private API.

Some fantastic work on this topic at this blog, and a couple great github projects linked: http://blog.steventroughtonsmith.com/2010/02/apples-ibooks-dynamic-page-curl.html