CODEWITHSUNDEEP
objective-cnsdictionary
Mirek
Mirek

Reputation: 500

NSDictionary order of keys and values

I know that in NSDictionary, there are no guarantees about the order of items when enumerating.

However, is it safe to expect that [[myDictionary allValues] objectAtIndex:index] will always be the matching value of key [[myDictionary allKeys] objectAtIndex:index]? (supposing that the dictionary is immutable).

Upvotes: 4

Views: 1239

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726509

Even if there is a very good chance that the two are going to be in the same order, Apple can change it at any time, because there is simply no guarantee of the order.

If you need two NSArrays, one with keys and one with values, with "parallel" indexes, a better approach to this would be building these arrays yourself by enumerating key-value pairs of the dictionary, and adding them to the two arrays that you build:

NSMutableArray *keys = [NSMutableArray array];
NSMutableArray *vals = [NSMutableArray vals];
[dict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
    [keys addObject:key];
    [vals addObject:obj];
}];

You can also get keys separately, and then get values in an array with parallel indexing by calling objectsForKeys:notFoundMarker: method:

NSArray *keys = [dict allKeys];
// In the call below, the marker [NSNull null] will not be used, because we know
// that all keys will be present in the dictionary.
NSArray *vals = [dict objectsForKeys:keys notFoundMarker:[NSNull null]];

Upvotes: 2

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