textfield 限制长度

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {int MAX_LENGHT = 5;    if([string isEqualToString:@"\n"])    {        [textField resignFirstResponder];        return FALSE;    }    else if(textField.text.length > MAX_LENGHT-1)    {        if([string isEqualToString:@""] && range.length == 1)        {            return TRUE;        }        else        {            return FALSE;        }    }    else    {        return TRUE;    }}