Looking for an elgant way to check if a Key exsists in a dictionary

Question

Possible Duplicate:
How to check if an NSDictionary or NSMutableDictionary contains a key?

I can get the an array of the Keys (strings) from the dictionary then loop through it doing a string compare with the Key i want to check for and see if that dictionary contains the key I seek.

But is there a more elegant want to check if the key exists in the dictionary?

        NSArray * keys = [taglistDict allKeys];
        for (NSString *key in keys) 
        {
           // do string compare etc
        }

-Code

2014 answer: http://stackoverflow.com/a/22001925/294884 – Fattie Apr 16 '14 at 13:18 — Fattie, Apr 16 '14 at 13:18

trojanfoe · Accepted Answer · 2013-07-05T05:32:25.007

37

An NSDictionary cannot contain nil values, so you can simply use [NSDictionary objectForKey:] which will return nil if the key does not exist:

BOOL exists = [taglistDict objectForKey:key] != nil;

EDIT: As mentioned by @OMGPOP, this also works using Objective-C literals using the following syntax:

NSDictionary *dict = @{ @"key1" : @"value1", @"key2" : @"value2" };

if (dict[@"key3"])
    NSLog(@"Exists");
else
    NSLog(@"Does not exist");

Prints:

Does not exist

edited Jul 05 '13 at 05:32

answered Jul 25 '12 at 15:24

trojanfoe

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what about modern objc? if i use dict[@"key"] it will crash – OMGPOP Jul 05 '13 at 03:10
this does not work for me . gives error . – Moxarth Jun 09 '17 at 09:36
Added information about 'an NSDictionary cannot contain nil values' : if you want a key with 'nothing' as a value, just put the object [NSNULL null]. – XLE_22 Jul 11 '17 at 13:41

score 10 · Answer 2 · answered Jul 25 '12 at 15:26

10

Trojanfoe is likely better, but you could also do:

[[taglistDict allKeys]containsObject:key]

answered Jul 25 '12 at 15:26

Eric

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score -2 · Answer 3 · edited Apr 13 '16 at 09:34

-2

Assuming the key is of type NSString and keys is a dictionary, then you should instead be using something like:

if [keys containObject:key] {
 // do something
}

edited Apr 13 '16 at 09:34

AlBlue

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answered Jul 25 '12 at 15:25

MrBr

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Looking for an elgant way to check if a Key exsists in a dictionary

3 Answers3