Objective-C property that is readonly publicly, but has a private setter

Question

I'd like to use the @property syntax to declare a synthesized property that is publicly readonly but has a setter that can be called privately from within the class.

Since it's Objective-C, this basically means that the setFoo: method would be synthesized, but calling it outside of the class itself would result in a warning (unrecognized selector). To trigger the warning I have to declare the property readonly; is there any way to force a synthesized setter that is only available within the class?

score 116 · Accepted Answer · edited Jun 30 '15 at 00:23

116

I think what you're looking for are called class extensions. You would declare the property read-only in the header:

@interface MyClass : NSObject {
}

@property (readonly, assign) NSInteger myInteger;

@end

Then redeclare in your class extension in the implementation file:

@interface MyClass ()

@property (readwrite, assign) NSInteger myInteger;

@end


@implementation MyClass

@end

For more check out Apple's documentation

edited Jun 30 '15 at 00:23

Lukas Spieß

2,478
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answered Feb 15 '11 at 19:00

Sean Rich

2,338
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1

You're correct, see also http://stackoverflow.com/questions/743586/synthesizing-properties-in-categories/3251621#3251621 – Adam Ernst Feb 15 '11 at 19:17
3

This is a great way to leverage the convenience of properties while maintaining necessary encapsulation. :) Love this capability. – CIFilter Feb 15 '11 at 21:03
5

Updated documentation link: http://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/CustomizingExistingClasses/CustomizingExistingClasses.html#//apple_ref/doc/uid/TP40011210-CH6-SW3 – Aaron Brager May 16 '13 at 17:58
1

Did anyone actually test this? Attempting to set the property using dot notation gets a compiler error (good), but using the setMyInteger: method only gets a compiler warning, and when the app is run the "readonly" property does get changed. – jk7 Jun 14 '16 at 01:25
1

@jk7 That is correct behavior; the compiler is telling you you are doing it wrong. The runtime is "free" to violate this. – bbum Dec 05 '19 at 20:52

score 1 · Answer 2 · answered May 10 '18 at 08:06

I might be late, but without extension i did using the following technique

@interface MyClass : NSObject {
 NSString * name;
}

@property (readonly, strong) NSString * name;

@end

on the other hand in implementation file

@implementation MyClass
 @synthesize name;

 - (id)initWithItems:(NSDictionary *)items {
self = [super init];
if(self)
{ 
  name = @"abc";
}

return self;
}

@end

doing so it will set your value and will be accessible as readonly. Thanks.

Objective-C property that is readonly publicly, but has a private setter

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