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.

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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.

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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