iOS - How to create Category with private methods

Question

I am in the process of creating a category for the class MKPolygon. You can find the reference to this class here. I have two public class methods that I want to make "public" and a handful of "private" methods to handle some of the internals. The reason I want to do this is because, as you can see, the methods available for this class are class methods and I want to continue with being in line with this by offering class methods which will both be returning (MKPolygon *). Also, there will be a lot of work that I will be writing and not breaking up the tasks would go against good coding practices and of course hard to test and read - this is especially important as I will be contributing this to github.

Here is my header and implementation file that was created when creating a new category in XCode. I am going to make the methods generic for now to get my point across:

MKPolygon+MKPolygonStuff.h

#import <MapKit/MapKit.h>

@interface MKPolygon (MKPolygonStuff){

}
+(MKPolygon *)polygon:(MKPolygon *)poly1 doStuff:(MKPolygon *)poly2 onMap:(MKMapView *)map;
+(BOOL)polygon:(MKPolygon *)poly1 doesThisThing:(MKPolygon *)poly2;

@end

MKPolygon+MKPolygonStuff.m

@interface MKPolygon(){


}

+(void)calculateStuff;

@end

@implementation MKPolygon (MKPolygonStuff)

+(void)calculateStuff{



}
+(MKPolygon *)polygon:(MKPolygon *)poly1 doStuff:(MKPolygon *)poly2 onMap:(MKMapView *)map{

  //do stuff and call other class methods to break up tasks
  //[self calculateStuff];

 }

+(BOOL)polygon:(MKPolygon *)poly1 doesThisThing:(MKPolygon *)poly2{

    //returns boolean
    //possibly call other class methods do some internals.
}

In my implmentation file my interface had something within the parenthesis but it gave me the following warning:

"Duplicate definition of category on interface..."

So i decided that i would just leave the parenthesis empty after reading a couple of other threads in here regarding this issue. Also doing this would allow me to have instance variables that I will most definitely need that I dont want to be made "public".

Now I have a warning that is located under the implementation section next to +(void)calculateStuff.

"Category is implementing a method which will also be implemented by its primary class".

I searched this warning around the net to see what would cause this warning and it seems that you would get this warning if the compiler recognizes that you will be overriding some built in functionality to the class. The thing is, is that there isn't a calculateStuff method in the MKPolygon class, so I am unsure why i am getting this warning. Is there something here that I am doing wrong, if anything and generally, do I have everything set up right here with that I want to do? Obviously, my private methods have to be class methods as well since you can't call instance methods from class methods.

Would appreciate any comments/suggestions/corrections here.

Answer 1

If calculateStuff is a private method that is only used in the implementation block of the MKPolygon (MKPolygonStuff) category then you need not declare that method in an interface at all.

Just remove @interface MKPolygon() ... @end from "MKPolygon+MKPolygonStuff.m".

With current Xcode/clang versions, you even need not forward declare a method that is defined and used inside an implementation block.