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

Question

In a iOS app, I needed a property which is . 。 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 part in the with respect to 's answer here , but compiler showed no warning or error when I used it as str = [[NSString alloc] initWithString:@"hello"] in the !! 的答案的部分在这里 ，但是编译器没有显示警告或错误，当我用它作为str = [[NSString alloc] initWithString:@"hello"]在 !!

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

I am using Xcode 5.1.1 我使用的是Xcode 5.1.1

Answer 1

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.