Question

I’ m trying to iterate NSDictionary via the for in loop. But I want it to begin iteration from the end of this collection to its beginning. How can I implement this reversion?

Answer 1

Mmm… the problem is that NSDictionary are unordered by nature.

So, a possible solution is make an NSArray with the keys, reverse that array with “reverseObjectEnumerator” and then make a loop over the array and use the keys on dictionary.

Something like this:

NSDictionary *_dict = [NSDictionary dictionaryWithObjectsAndKeys:
                       @"firstValue",@"firstKey",
                       @"secondValue",@"secondKey",
                       @"thirdValue",@"thirdKey",
                       nil];

NSArray *keysNormal   = [_dict allKeys];
NSArray *keysReversed = [[[_dict allKeys] reverseObjectEnumerator] allObjects];

for(NSString *str in keysNormal)
{
    NSLog(@"%@", [_dict objectForKey:str]);
}

for(NSString *str in keysReversed)
{
    NSLog(@"%@", [_dict objectForKey:str]);
}

The log is:

• thirdValue
• secondValue
• firstValue
• firstValue
• secondValue
• thirdValue