Question

I am creating a new file using Xcode’s navigation based application and I see that the .m file has these lines:

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

Why is that declared on .m and not on .h itself?

wouldn’t it be easier to just put one line (this one below) on the header file?

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

I have seen this kind of approach in other codes. I am still learning Objective-C and I wonder why is that.

thanks.

Answer 1

By not putting it into the public interface of the class, you’re essentially making a method private (it doesn’t prevent people outside of your class from calling it if they really want to, but at least it causes a compiler warning).

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

is a class extension (= an anonymous category; a “normal” category would have a category name in between the ()). It purpose is to declare the private methods (otherwise you’d get a compiler warning if you’re trying to call configureCell:atIndexPath: in the .m file prior to its implementation).

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