读取xml报16进制字符错误，因为xml文件中包括特殊字符，如u0018,造成解析错误
解析方法：剔除xml特殊字符再读取

  private string RemoveInvalidXmlChars(string text)
        {
            var validXmlChars = text.Where(ch => XmlConvert.IsXmlChar(ch)).ToArray();
            return new string(validXmlChars);
        }

private void OnRecvMessage(string Message) //接收到插件发来的消息触发该事件
        {
            try
            {
                RtxMessage rm = new RtxMessage();

                StringReader sr1 = new StringReader(RemoveInvalidXmlChars(Message.Content));//避免0/这种异常字符
                XmlReader xr1 = XmlTextReader.Create(sr1); // xr1's type is XmlTextReaderImpl

                while (xr1.Read())
                {
                    if (xr1.Name == "Item")
                    {

                        switch (xr1["Key"])
                        {
                            case "Mode": { if (xr1.Read()) { rm.Mode = xr1.Value; }; break; }
                            case "Content": { if (xr1.Read()) { rm.Content = GetContent(xr1.Value); }; break; }
                            case "Initiator": { if (xr1.Read()) { rm.Initiator = xr1.Value; }; break; }
                            case "Key": { if (xr1.Read()) { rm.Key = xr1.Value; }; break; }
                            case "Title": { if (xr1.Read()) { rm.Title = xr1.Value; }; break; }
                            case "im_message_id": { if (xr1.Read()) { rm.im_message_id = xr1.Value; }; break; }
                            default: { break; }
                        }
                    }
                }

            }
            catch (COMException xe)
            {

            }

        }