iPhone – Why is it in .m declared some methods instead .h?

@interface RootViewController ()
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
@end

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;

@interface RootViewController ()
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath; 
@end

I am using Xcode’s navigation-based application to create a new file, and I see that the .m file contains the following lines:

 @interface RootViewController ()
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
@end

Why is it declared on .m but not on. H itself?

Will it be easier to put a line (the following line) in the header file?

- (void)configureCell: (UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath; 

I have seen this method in other code. I am still learning Objective-C, I want to know why this is the case.

Thank you.

By not putting it into the public interface of the class, you are actually a private method (it won’t stop people outside your class if they really want to call it, But at least it will cause the compiler to warn).

@interface RootViewController ()
- (void)configureCell:(UITableViewCell *)cell atIndexPath:( NSIndexPath *)indexPath;
@end

is a class extension (=anonymous category; the “normal” category has category names between (). Its purpose is to declare private methods (otherwise, if If you try to call configureCell:atIndexPath: in the .m file before implementation, you will receive a compiler warning).

You can read more about categories and class extensions in the developer documentation

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