NSDictionary: convert NSString keys to lowercase to search a string on them

Question

I'm developing an iPhone application.

I use a NSDictionary to store city's names as key, and population as value. I want to search the keys using lowercase.

I've using this:

NSDictionary *dict;

[dict objectForKey:[[city stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] lowercaseString]];

But, it doesn't work.

I know, I can do a for, convert keys to lowercase and compare with city.

Is there any other way to do that? Maybe, with a NSDictionary method.

UPDATE
The NSDictionary is loaded from a property list.

Thank you.

Answer 1

I use this method in an NSDictionary category.

@implementation NSDictionary (MyCategory)
- (NSDictionary *)dictionaryWithLowercaseKeys {
    NSMutableDictionary *result = [NSMutableDictionary dictionaryWithCapacity:0];
    NSString *key;

    for (key in self) {
        [result setObject:[self objectForKey:key] forKey:[key lowercaseString]];
    }

    return result;
}
@end