CODEWITHSUNDEEP
iosobjective-cproperties
Sibir
Sibir

Reputation: 313

Properties in Objective C (readwrite for self and readonly for others)

In a iOS app, I needed a property which is readonly for other classes but readwrite for self calls. So I followed this question and formed my code as,

In .h:

@interface TheClassName : NSObject {
     NSString* str;
}
@property(nonatomic, retain, readonly) NSString* str;
@end

In .m:

@interface TheClassName()
@property(nonatomic, retain, readwrite) NSString* str;
@end

@implementation TheClassName
-(id)init {
     if(self = [super init]) {
          str = [[NSString alloc] initWithString:@"hello"];
     }
     return self;
}
@end

This procedure is valid also according to Apple Documentation. But I tried experimenting on my code and the problem started.

All I did is ignored the @interface part in the .m file with respect to Seva Alekseyev's answer here, but compiler showed no warning or error when I used it as str = [[NSString alloc] initWithString:@"hello"] in the .m file !!

I mean, the property is set to be readonly, so the statement should have produced an error, but it didn't. WHY??

NOTE: I am using Xcode 5.1.1

Upvotes: 1

Views: 787

Answers (1)

trojanfoe
trojanfoe

Reputation: 122381

This code:

str = [[NSString alloc] initWithString:@"hello"];

doesn't call the property setter, it references the instance variable you defined directly:

@interface TheClassName : NSObject {
     NSString* str;
}

and, by default, the backing instance variable will be called _str, so you should remove that instance variable definition and refer to _str directly (if you don't want to create a readwrite version of the property). As it currently stands the property str won't refer to the instance variable str without explicitly using a @synthesize str = str; statement.

Upvotes: 3

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