Question

I want to validate my text field with a YYYY format, meaning a user can only enter a four digit number like a year. There are seven text fields including this text field; I only want this text field to require validation.

Answer 1

Here are sample for validate text field.

    - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
    {
       If(textField == myTextField)
       {

         if ([textField length] > 4)
         {
             return NO;
         }
        NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
        [numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];

        NSNumber* candidateNumber;

        NSString* candidateString = [textField.text stringByReplacingCharactersInRange:range withString:string];

        range = NSMakeRange(0, [candidateString length]);

        [numberFormatter getObjectValue:&candidateNumber forString:candidateString range:&range error:nil];

        if (([candidateString length] > 0) && (candidateNumber == nil || range.length < [candidateString length])) {

            return NO;
        }
        else 
        {
            return YES;
        }
    }
    }