Subclass NSString - iphone

Question

I want to add a property to a NSString object. For this reason I want to subclass it.
I try to make something like this:
#interface MyString : NSString
#property (nonatomic) NSInteger userId;
#end
so then I can do
MyString *testString = [[MyString alloc] init];
testString = [MyString stringWithFormat:#"hello"];
testString.userId = 2;
NSLog(#"testString: %#", testString); //-> Want it to return "testString: hello"
NSLog(#"userId: %d", testString.userId); //-> Want it to return "userId: 2"
I don't know how to subclass NSString (create storage facilities, override some methods (length, characterAtIndex). Have an idea?

Answer 1

Don't try to subclass NSString to do this. Create an entirely new class that is a subclass of NSObject and give it 2 properties (and a set of methods to access the properties if you want to).
Trying to use NSString is overly complicated and not appropriate.
For this line:
NSLog(#"testString: %#", testString);
all you need to do is implement the description method on your custom class to return the string property. Then the string will be printed when you use NSLog.

Answer 2

Subclassing class cluster classes is tricky, as you've discovered. Which is why, generally, it is pretty much never done.
Instead, create a class that encapsulates two strings; the string that would point to #"hello" in your example and the userId.
#interface MyThingy:NSObject
#property(copy) NSString *stringData;
#property(copy) NSString *userId;
#end
... etc ...
This will be far more flexible and it will be easier to refactor in the future.
BTW, this doesn't make sense:
MyString *testString = [[MyString alloc] init];
testString = [MyString stringWithFormat:#"hello"];
Under manual retain/release, it is a leak. Under ARC, it is a purposeless allocation.

Answer 3

Why don't you use NSMutablestring in this you can use appendString method in which you can add your any stringValue and then just pass the same to your string.

Answer 4

Try this category. You can add any kind of custom object to anything coming from NSObject - basically any class - by use of a key. Retrieve the object using that key. I think I got this from someone (found it) here on stackoverflow.
Header:
//
// NSObject+arbitraryobjectonanynsobjectlol.h
//
//
// Created by someone on 2/21/14.
// Copyright (c) 2014 someone. All rights reserved.
//
#import <Foundation/Foundation.h>
// https://stackoverflow.com/a/10319083/129202
#interface NSObject (arbitraryobjectonanynsobjectlol)
- (id)associativeObjectForKey: (NSString *)key;
- (void)setAssociativeObject: (id)object forKey: (NSString *)key;
#end
And the implementation:
//
// NSObject+arbitraryobjectonanynsobjectlol.m
// someone
//
// Created by someone on 2/21/14.
// Copyright (c) 2014 someone. All rights reserved.
//
#import "NSObject+arbitraryobjectonanynsobjectlol.h"
#import <objc/runtime.h>
#implementation NSObject (arbitraryobjectonanynsobjectlol)
static char associativeObjectsKey;
- (id)associativeObjectForKey: (NSString *)key {
NSMutableDictionary *dict = objc_getAssociatedObject(self, &associativeObjectsKey);
return [dict objectForKey: key];
}
- (void)setAssociativeObject: (id)object forKey: (NSString *)key {
NSMutableDictionary *dict = objc_getAssociatedObject(self, &associativeObjectsKey);
if (!dict) {
dict = [[NSMutableDictionary alloc] init];
objc_setAssociatedObject(self, &associativeObjectsKey, dict, OBJC_ASSOCIATION_RETAIN);
} [dict setObject: object forKey: key];
}
#end