Forcing UITextField to have first character as numeric and second as alphanumeric

Question

I'm trying to figure out a way to 'force' the UITextField to follow a set method. For example:

I have successfully limited it to only accept 4 characters as a max but I need it to set the 4 character limit to be first character "Numeric" second character "AlphaNumeric" Third / Fourth to be "Numeric" for example : 1Z11

I also can't figure out if you can force capitalised lettering or not like you can via ASCII or VBA.

Any help would be perfect, I have looked around but all I can only find is how to force one or the other (all numeric or all alphanumeric).

Kindest Regards Jamie

-Edit one-

I have no code for the limiting of the characters as I said above I can only find ways to limit one or the other so I have no code inputted yet (Can link to the stack posts if you want?).

how about editing your question to show how you are currently limiting it to only accepting certain characters? i.e. show code. — Michael Dautermann, May 20 '14 at 15:27
For the capitalised lettering : http://stackoverflow.com/questions/2027164/iphone-force-textbox-input-to-upper-case — Guntis Treulands, May 20 '14 at 15:28
Thank you @GuntisTreulands for this, this looks like it will work perfectly. — JamieB, May 20 '14 at 15:52
@MichaelDautermann I have no code for the limiting of the characters as I said above I can only find ways to limit one or the other so I have no code inputted yet (Can link to the stack posts if you want?). — JamieB, May 20 '14 at 15:52

streem · Answer 1 · 2014-05-20T15:50:25.333

Try implementing something like this for the delegate method :

 - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    if (range.location != 1) {
        NSScanner *scanner = [NSScanner scannerWithString:string];
        BOOL isNumeric = [scanner scanInteger:NULL] && [scanner isAtEnd];
        return isNumeric;
    }else if (range.location<4){
        return YES;
    }
    return NO;
 }

Bobj-C · Answer 2 · 2014-05-20T16:05:36.967

Please try the below

NSCharacterSet *numeric = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
NSCharacterSet *alphaNumberSet = [[NSCharacterSet alphanumericCharacterSet] invertedSet];


 - (BOOL)textField:(UITextField *)field shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)characters
{       

     //allow backspace
       if ([characters isEqualToString:@""])
{
    return YES;
}
       switch (field.text.length) {
            case 0:
            case 2:
            case 3:
        {
             BOOL retVal =  ([characters rangeOfCharacterFromSet:numeric].location == NSNotFound);
            return retVal;
        }
            break;
         case 1:
        {
            BOOL retVal =  ([characters rangeOfCharacterFromSet:alphaNumberSet].location == NSNotFound);
            return retVal;

        }
        default:
            return NO;
            break;
    }

}

Forcing UITextField to have first character as numeric and second as alphanumeric

2 Answers2