NSString Length - Special Characters

Question

I have a UITextField that users will be entering characters into. It is as simple as, how can I return it's actual length? When the string contains A-Z 1-9 characters it works as expected but any emoji or special characters get double counted.

In it's simplest format, this just has an allocation of 2 characters for some special characters like emoji:

NSLog(@"Field '%@' contains %i chars", myTextBox.text, [myTextBox.text length] );

I have tried looping through each character using characterAtIndex, substringFromIndex, etc. and got nowhere.

As per answer below, exact code used to count characters (hope this is the right approach but it works..):

NSString *sString = txtBox.text;

__block int length = 0;
[sString enumerateSubstringsInRange:NSMakeRange(0, [sString length]) 
                        options:NSStringEnumerationByComposedCharacterSequences
                        usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {

                            length++;                                
                        }];

NSLog(@"Total: %u", length );

Answer 1

The [myTextBox.text length] returns the count of unichars and not the visible length of the string. é = e+´ which is 2 unichars. The Emoji characters should contain more the 1 unichar.

This sample below enumerates through each character block in the string. Which means if you log the range of substringRange it can longer than 1.

__block NSInteger length = 0;
[string enumerateSubstringsInRange:range
                           options:NSStringEnumerationByComposedCharacterSequences
                        usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
    length++;
}];

You should go and watch the Session 128 - Advance Text Processing from 2011 WWDC. They explain why it is like that. It's really great!

I hope this was to any help.
Cheers!