CODEWITHSUNDEEP
iphoneobjective-ccocoansdictionary
Thaurin
Thaurin

Reputation: 195

Is NSDictionary key order guaranteed the same as initialized if it never changes?

I've run into the same problem as found in this question. However, I have a follow-up question. I seem to be in the same situation as the original asker: I have a plist with a hierarchy of dictionaries that define a configuration screen. These are not mutable and will stay the same throughout the application. Since the original discussion seems to focus on problems arising from mutating the dictionary, I must ask for comfirmation: is the order of a dictionary guaranteed the same as they are in the plist, i.e. as it is read (with initWithContentsOfFile)? Can I use allKeys on it in this case to get a correct-order array of keys if the dictionary never changes?

Upvotes: 6

Views: 6410

Answers (4)

Jens Ayton
Jens Ayton

Reputation: 14558

Nothing at all is guaranteed about order. It’s not even guaranteed that iterating over a dictionary twice will give you the keys in the same order.

Upvotes: 3

stefanB
stefanB

Reputation: 79920

I would not assume that the keys will be in any kind of order because allKeys does not guarantee order.

Internally, NSDictionary uses a hash table.

From allKeys description:

The order of the elements in the array is not defined.

If you want to display values in some order then get the keys, sort the keys array and then get the value for each key.

Upvotes: 3

Dave DeLong
Dave DeLong

Reputation: 243156

If you need an NSDictionary that maintains order, take a look at CHDataStructure's CHOrderedDictionary, which does exactly that. I use it all the time.

Upvotes: 7

dreamlax
dreamlax

Reputation: 95385

No, the keys are not likely to appear in the same order as your plist file. I can't look under the hood, but I would guess that the keys are ordered in whatever way that provides an efficient look-up. The documentation for allKeys says that the order of the elements in the array is not defined.

Upvotes: 8

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