Implementing maxlength for UITextField. This will prevent any character sequence from being inserted that would make the textfield's text exceed the maxlength. If you paste in multicharacter sequences that will make the field exceed its max length, the entire sequence will be rejected.

gistfile1.m

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
  NSInteger result = textField.text.length;
  result -= range.length;
  result += string.length;
  return result <= MAX_LENGTH;
}