设置，获取和删除Cookies

        #region 保存用户名的Cookie
        /// <summary>
        /// 设置Cookie
        /// </summary>
        /// <param name="cookieName"></param>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="expires"></param>
        /// <returns></returns>
        public HttpCookie SetCookie(string cookieName, string key, string value, DateTime? expires)
        {
            HttpResponse response = System.Web.HttpContext.Current.Response;
            if (response != null)
            {
                HttpCookie cookie = response.Cookies[cookieName];
                if (cookie != null)
                {
                    if (!string.IsNullOrEmpty(key) && cookie.HasKeys)
                        cookie.Values.Set(key, value);
                    else
                        if (!string.IsNullOrEmpty(value))
                            cookie.Value = value;
                    if (expires != null)
                        cookie.Expires = expires.Value;
                    response.SetCookie(cookie);
                }
                return cookie;
            }
            else
            {
                return null;
            }
        }

        /// <summary> 
        /// 获得Cookie 
        /// </summary> 
        /// <param name="cookieName"></param> 
        /// <returns></returns> 
        public HttpCookie GetCookie(string cookieName)
        {
            bool isReusable = HttpContext.CurrentHandler.IsReusable;
            HttpRequest request = System.Web.HttpContext.Current.Request;
            if (request != null)
                return request.Cookies[cookieName];
            return null;
        }
        /// <summary>
        /// 删除Cookies
        /// </summary>
        /// <param name="cookieName"></param>
        /// <param name="key"></param>
        public static void RemoveCookie(string cookieName, string key)
        {
            HttpResponse response = System.Web.HttpContext.Current.Response;
            if (response != null)
            {
                HttpCookie cookie = response.Cookies[cookieName];
                if (cookie != null)
                {
                    if (!string.IsNullOrEmpty(key))
                        cookie.Values.Remove(key);
                    else
                        response.Cookies.Remove(cookieName);
                }
            }

        }
        #endregion