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How can I declare a private property within a named category?

I know about the possibility of declaring private properties on a class by putting them inside an unnamed category on that class declared in the implementation (.m) file of that class. That's not what I want to do.

I'm dealing with a named category on a class that adds some functionality to that class. For this functionality, it would help me very much to have a private property to use in my category - so the usual way of achieving this (described above) doesn't seem to work for me. Or does it? Please enlighten me!

like image 387
Jan Z. Avatar asked Jan 18 '13 13:01

Jan Z.


1 Answers

Inside your category's implementation file, declare another category and call it something like MyCategoryName_Private, and declare your private properties there. Provide implementations of the -propertyName and -setPropertyName: methods using associated objects.

For example, your implementation file might look like this:

#import "SomeClass+MyCategory.h"
#import <objc/runtime.h>

@interface SomeClass (MyCategory_Private)

@property (nonatomic, strong) id somePrivateProperty;

@end

@implementation SomeClass (MyCategory_Private)

static void *AssociationKey;

- (id)somePrivateProperty 
{
    return objc_getAssociatedObject(self, AssociationKey);
}

- (void)setSomePrivateProperty:(id)arg
{
    objc_setAssociatedObject(self, AssociationKey, arg, OBJC_ASSOCIATION_RETAIN);
}

@end

@implementation SomeClass (MyCategory)

// implement your publicly declared category methods

@end
like image 93
Carl Veazey Avatar answered Sep 29 '22 06:09

Carl Veazey