How can i get Original order of NSDictionary/NSMutableDictionary?

Question

i have created NSMutableDictionary with 10 keys.Now i want to access NSMutableDictionary keys in a same order as it was added to NSMutableDictionary (using SetValue:* forKey:* );

How can i achieve that ?

Solution 1

If you absolutely must use a dictionary container, you have to use a key that is sortable by the order in which you add key-value pairs. Thus, when creating your dictionary, you use a key that is an auto-incrementing integer or similar. You can then sort on the (integer) keys and retrieve the values associated with those keys.

If you do all of that, however, you may as well just use an NSMutableArray and add values to the array directly! It will be much faster and require less code. You just retrieve objects in order:

for (id obj in myArray) { /* do stuff with obj... */ }

Solution 2

NSMutableDictionary can't do that. Take a look at e.g. Matt Gallaghers OrderedDictionary.

Solution 3

I wrote a quick method to take a source array (of objects that are all out of order) and a reference array (that has objects in a desired (and totally arbitrary) order), and returns an array where the items of the source array have been reorganized to match the reference array.

- (NSArray *) reorderArray:(NSArray *)sourceArray toArray:(NSArray *)referenceArray
{
    NSMutableArray *returnArray = [[NSMutableArray alloc] init];
    for (int i = 0; i < [referenceArray count]; i++)
    {
        if ([sourceArray containsObject:[referenceArray objectAtIndex:i]])
        {
            [returnArray addObject:[arrReference objectAtIndex:i]];
        }
    }
    return [returnArray copy];
}

Note that this is very fragile. It uses NSArray's containsObject: method, which ultimately will call NSObject's isEqual:. Basically, it should work great for arrays of NSStrings, NSNumbers, and maybe NSDates (haven't tried that one yet), but outside of that, YMMV. I imagine if you tried to pass arrays of UITableViewCells or some other really complex object, it would totally sh*t itself, and either crash or return total garbage. Likewise if you were to do something like pass an array of NSDates as the reference array and an array of NSStrings as the source array. Also, if the source array contains items not covered in the reference array, they'll just get discarded. One could address some of these issues by adding a little extra code.

All that said, if you're trying to do something simple, it should work nicely. In your case, you could build up the reference array as you are looping through your setValue:forKey:.

NSMutableArray *referenceArray = [[NSMutableArray alloc] init];
NSMutableDictionary *yourDictionary = [[ NSMutableDictionary alloc] init];

for (//whatever you are looping through here)
{

    [yourDictionary setValue://whatever forKey:key];
    [referenceArray addObject:key];

}

Then, when you want to loop over your items in the order they came in, you just

for (NSString *key in [self reorderArray:[myDict allKeys] toArray:referenceArray])