What constitutes a private API in an iPhone app?

Question

I'm fairly new to Objective-C and am confused on what falls under the unbrella of a "private API" that could cause Apple to reject my app. Does this include adding methods to existing classes? For example, I found some code on stackoverflow to recolor the tab bar icons for UITabBars with this extension to the UITabBarItem class. Is this considered a "private API"? If not, what does?

@interface UITabBar (ColorExtensions)
- (void)recolorItemsWithImage:(UIImage *)image shadowColor:(UIColor *)shadowColor shadowOffset:(CGSize)shadowOffset shadowBlur:(CGFloat)shadowBlur;
@end

Answer 1

No, categories added by user code are not "private." Private APIs are Apple's internal APIs, which are undocumented. Methods are private if they aren't in the header files and aren't in the developer documentation. (As a rule of thumb, if you don't get any compiler warnings, you aren't using private APIs.)

Answer 2

The above is probably an Objective-C category that extends the UITabBar class with new methods. This is perfectly kosher. You can even overwrite existing methods with categories, although this isn't recommended.

In general, private methods will often have underscores in front of them. You also don't want to use private classes that Apple reserves for large UI objects, such as the private components within a UIWebView. You don't want to use these or your app will get rejected.

Anything that you see in a header file in the Frameworks in your project is "public" and usable. It's a good idea to thumb through the header if you really want to know everything about the class, anyway.