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as the title, when I insert element to a dictionary in objective-c (in order like: k1, k2, k3), is there any guarantee that when I enumerate it like:
for ( k in dictionary ){
// output the k - value
}
it would show in the same order?
914
You don't access sequentially to a dictionary as you would when, for example, iterating a list or array. You access by having a key, then finding whether there's a value for that key on the dictionary and what is it.
Objective-C Dictionary Object classes allow data to be stored and managed in the form of key-value pairs where both the key and the value are objects.
An NSDictionary will retain it's objects, and copy it's keys.
So if you need to add arrays for more than one key you might do this: Given an array of two keys: NSArray *keys = [NSArray arrayWithObjects:@"key0",@"key1", nil]; And a dictionary...
No, NSDictionary does not maintain the insertion order of its keys.
If you need a dictionary that maintains insertion order, I'd suggest using the CHDataStructures framework, which has a CHOrderedDictionary class (it's a descendent of NSMutableDictionary). The documentation for CHOrderedDictionary says:
A dictionary which enumerates keys in the order in which they are inserted.
The following additional operations are provided to take advantage of the ordering:
-firstKey
-lastKey
-keyAtIndex:
-reverseKeyEnumerator
Key-value entries are inserted just as in a normal dictionary, including replacement of values for existing keys, as detailed in -setObject:forKey:. However, an additional structure is used in parallel to track insertion order, and keys are enumerated in that order. If a key to be added does not currently exist in the dictionary, it is added to the end of the list, otherwise the insertion order of the key does not change.
171
NSDictionary's keys aren't kept in order, but you can get them and sort them, E. G:
for (key in [[myDict allKeys] sortedArrayUsingSelector:@selector(compare:)])
...
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