How to rename a Key in NSMutableDictionary? - iphone

Question

I am having a NSMutableDictionary. I have to dynamically rename any Key in the dictionary to a new value, in my code.. I can't find any built-in API to do this..
How can I do this? Is there any built-in API available to do this?
Thanks everyone..

Answer 1

// assumes that olkdey and newkey won't be the same; they can't as
// constants... but...
[dict setObject: [dict objectForKey: #"oldkey"] forKey: #"newkey"];
[dict removeObjectForKey: #"oldkey"];
Think about what "directly editing an existing key" means. A dictionary is a hash; it hashes the contents of the keys to find a value.
What happens if you were to change the contents of a key? The key would need to be rehashed (and the dictionary's internal structures re-balanced) or the value would no longer be retrievable.
Why do you want to edit the contents of a key in the first place? I.e. what problem does that solve that the above does not?

Answer 2

This should work:
- (void) renameKey:(id<NSCopying>)oldKey toKey:(id<NSCopying>)newKey{
NSObject *object = [dictionary objectForKey:oldKey];
[object retain];
[dictionary removeObjectForKey:oldKey];
[dictionary setObject:object forKey:newKey];
[object release];
}
This does exactly the same as bbum's answer but, if you remove the old key first (like in this example) then you have to retain the object temporarily otherwise it might get deallocated in the way ;)
Conclusion: Unless you need explicitly to remove the old key first do as bbum.

Answer 3

#interface NSMutableDictionary (KAKeyRenaming)
- (void)ka_replaceKey:(id)oldKey withKey:(id)newKey;
#end
#implementation NSMutableDictionary (KAKeyRenaming)
- (void)ka_replaceKey:(id)oldKey withKey:(id)newKey
{
id value = [self objectForKey:oldKey];
if (value) {
[self setObject:value forKey:newKey];
[self removeObjectForKey:oldKey];
}
}
#end
This also handles the case where the dictionary doesn't have a value for the key nicely.

Answer 4

I have to navigate a complete JSON response object that holds fields, sub-dictionaries and sub-arrays. All because one of the JSON fields is called "return" which is an iOS reserved word, so can't be used with the JSONModel Cocoa Pod.
Here's the code:
+ (id) sanitizeJSON:(id) dictIn {
if (dictIn) //check not null
{
// if it's a dictionary item
if ([dictIn isKindOfClass:[NSDictionary class]])
{
NSMutableDictionary *dictOut = [dictIn mutableCopy];
// Do the fix replace "return" with "not_return"
if ([dictOut objectForKey: #"return"])
{[dictOut setObject: [dictIn objectForKey: #"return"] forKey: #"not_return"];
[dictOut removeObjectForKey: #"return"];}
// Continue the recursive walk through
NSArray*keys=[dictOut allKeys]; //get all the keys
for (int n=0;n<keys.count;n++)
{
NSString *key = [keys objectAtIndex:n];
//NSLog(#"key=%# value=%#", key, [dictOut objectForKey:key]);
if (([[dictOut objectForKey:key] isKindOfClass:[NSDictionary class]]) || ([[dictOut objectForKey:key] isKindOfClass:[NSArray class]]))
{
// recursive call
id sanitizedObject = [self sanitizeJSON:[dictOut objectForKey:key]];
[dictOut removeObjectForKey: key];
[dictOut setObject:sanitizedObject forKey:key];
// replace returned (poss modified) item with this one
}
}
return dictOut; //return dict
}
else if ([dictIn isKindOfClass:[NSArray class]]) //Or if it's an array item
{
NSMutableArray *tempArray = [dictIn mutableCopy];
// Do the recursive walk across the array
for (int n=0;n< tempArray.count; n++)
{
// if array item is dictionary
if (([[tempArray objectAtIndex:n] isKindOfClass:[NSDictionary class]]) || ([[tempArray objectAtIndex:n] isKindOfClass:[NSArray class]]))
{
// recursive call
id sanitizedObject = [self sanitizeJSON:[tempArray objectAtIndex:n]];
// replace with the possibly modified item
[tempArray replaceObjectAtIndex:n withObject:sanitizedObject];
}
}
return tempArray; //return array
}
return dictIn; //Not nil or dict or array
}
else
return dictIn; //return nil
}