C#在invoke的返回值为null时捕获soap消息

当下面的代理Web服务返回空值时，我需要将返回的soap消息存储在数据库中，与特定的用户ID相对应。 我当前正在将soap消息捕获到TraceExtension类中的文本文件中。但是由于属性元数据是常量，我无法在运行时将UserID传递给这个类。有什么解决办法吗

[ TraceExtensions.TraceExtension(), System.Web.Services.Protocols.SoapDocumentMethodAttribute("", Use = System.Web.Services.Description.SoapBindingUse.Literal)]
[return: System.Xml.Serialization.XmlElementAttribute("qualifyServicesResponse", Namespace = "")]
public qualifyServicesResponse qualifyServices([System.Xml.Serialization.XmlElementAttribute(Namespace = "")] qualifyServicesRequest qualifyServicesRequest, int UserID)
{
    object[] results = this.Invoke("qualifyServices", new object[] {
            qualifyServicesRequest, UserID});
    return ((qualifyServicesResponse)(results[0]));
}

TraceExtension类如下所示：

<AttributeUsage(AttributeTargets.Method)> _
Public Class TraceExtensionAttribute
    Inherits SoapExtensionAttribute

    Private m_filename As String = "C:\trace\log.xml"

End Class

---

最后，我在BeforeSerialize中使用message.GetInParameterValue来获取用户ID：

Public Overrides Sub ProcessMessage(ByVal message As SoapMessage)

    Select Case message.Stage
        Case SoapMessageStage.BeforeSerialize
            UserID = Convert.ToInt32(message.GetInParameterValue(1))
        Case SoapMessageStage.AfterSerialize
            WriteOutput(message)
        Case SoapMessageStage.BeforeDeserialize
            WriteInput(message)
        Case SoapMessageStage.AfterDeserialize
    End Select
End Sub

Public Overrides Sub ProcessMessage(ByVal message As SoapMessage)

    Select Case message.Stage
        Case SoapMessageStage.BeforeSerialize
            UserID = Convert.ToInt32(message.GetInParameterValue(1))
        Case SoapMessageStage.AfterSerialize
            WriteOutput(message)
        Case SoapMessageStage.BeforeDeserialize
            WriteInput(message)
        Case SoapMessageStage.AfterDeserialize
    End Select
End Sub