Asp.net 插入或更改查询字符串

 string InsertOrUpdateQueryStringItem(string key, string value)
        {
            if (Request.QueryString.HasKeys())
            {
                if (!Array.Exists<string>(Request.QueryString.AllKeys, (qs) => { return qs.Equals(key); }))
                {
                    return string.Format("{0}&{1}={2}", Request.RawUrl, key, value);
                }
                else
                {
                    System.Text.StringBuilder pathBuilder = new System.Text.StringBuilder(Request.Path);
                    pathBuilder.Append("?");
                    string keyValue;
                    string keyCurrent;
                    int handedCount = 0;

                    foreach (var k in Request.QueryString.AllKeys)
                    {

                        if (!k.Equals(key))
                        {
                            keyValue = Request.QueryString[k];
                            keyCurrent = k;
                        }
                        else
                        {
                            keyValue = value;
                            keyCurrent = key;
                        }

                        if (string.IsNullOrEmpty(keyValue))
                        {
                            continue;
                        }

                        if (handedCount++ != 0)
                        {
                            pathBuilder.AppendFormat("&{0}={1}", keyCurrent, keyValue);
                        }
                        else
                        {
                            pathBuilder.AppendFormat("{0}={1}", keyCurrent, keyValue);
                        }
                    }
                    return pathBuilder.ToString();
                }
            }
            return string.Format("{0}?{1}={2}", Request.Path, key, value);
        }