Determine whether proposed change to UITextField will exceed maximum text length

ShouldChangeCharactersInRange.m

-(BOOL)shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string textField:(UITextField *)textField maxLength:(NSUInteger)maxTextFieldLength
{
    NSUInteger oldLength = [textField.text length];
    NSUInteger replacementLength = [string length];
    NSUInteger rangeLength = range.length;
    NSUInteger newLength = oldLength - rangeLength + replacementLength;
    return newLength <= maxTextFieldLength;
}