NSDictionary Key For Value/Object?

Question

Can we get the key for an object in an NSDictionary by passing a particular value or object?

jscs · Accepted Answer · 2011-05-25T07:40:28.433

149

-[NSDictionary allKeysForObject:] returns an NSArray of all the keys whose objects match the passed object, where "match" is determined by isEqual:.

edited May 25 '11 at 07:40

answered May 25 '11 at 07:31

jscs

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but remember: it gives all keys for objects matching 'isEqual' not '==' – Kai Huppmann May 25 '11 at 07:36
@Kai: True. I should perhaps also add a note about it returning an `NSArray` although that should be clear from the method name. – jscs May 25 '11 at 07:38
2

If this isn't an FGITW question and answer, I don't know what is. Five upvotes just because I have a search shortcut in my browser. – jscs May 25 '11 at 07:57

AddisDev · Answer 2 · 2013-09-16T18:28:15.290

44

To answer you question in a more specific manner, use the following to get a key for a particular object:

NSString *knownObject = @"the object";
NSArray *temp = [dict allKeysForObject:knownObject];
NSString *key = [temp lastObject];

//"key" is now equal to the key of the object you were looking for

edited Sep 16 '13 at 18:28

answered May 01 '12 at 20:20

AddisDev

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In the case the object is not a string, replace NSString with the object class. This is self explanatory. – AddisDev Sep 06 '13 at 18:28
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You might prefer `lastObject` to `objectAtIndex:0` to avoid throwing an exception if there are no such keys. – Jesse Rusak Sep 06 '13 at 18:50
3

Or even `firstObject` if you are using the latest SDK – Abizern Feb 15 '14 at 14:16

score 3 · Answer 3 · edited Sep 25 '17 at 04:53

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This is how you can get a first key for object (in case it is an NSString):

NSArray *keys = [yourDic allKeysForObject:yourObject];
NSString *yourKey;
if ([keys count] > 0) {
   yourKey = keys[0];
}

This handles if the object is not found in in the dictionary.

edited Sep 25 '17 at 04:53

Alex Zavatone

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answered Mar 15 '13 at 15:47

Denis Kutlubaev

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NSDictionary Key For Value/Object?

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