Error : vb selectsinglenode object variable or with block variable not set

Question

Am getting error object variable or with block variable not set while SelectSingleNode from xml document

Here is my code

 sWC = My.Computer.FileSystem.ReadAllText("c:\inetpub\" & sServer & "\web.config")
    Dim xmlDoc = New XmlDocument()
    xmlDoc.Load("c:\inetpub\" & sServer & "\web.config")

  Dim nodeRegion = xmlDoc.CreateElement("add")
        nodeRegion.SetAttribute("key", sAppPool)
        nodeRegion.SetAttribute("value", "Sunday,12:00 AM")
        xmlDoc.SelectSingleNode("//appSettings").AppendChild(nodeRegion)
        xmlDoc.Save("c:\inetpub\" & sServer & "\web.config")

xmlDoc.SelectSingleNode("//appSettings") in this am getting "Nothing" as string

In my web.config i have

<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0"> 

xmlns in configuration section .

If i removed from "xmlns" from configuration tag i am able to update my web.config . if i kept this am getting object variable or with block variable not set error while SelectSingleNode from xml

Answer 1

Your XML has default namespace (namespace declared without prefix). Descendant elements inherit ancestor default namespace implicitly, unless otherwise specified. To access element in namespace, you need to map a prefix to point to the namespace uri, and then use that prefix in your XPath :

Dim xmlDoc = New XmlDocument()
xmlDoc.Load("c:\inetpub\" & sServer & "\web.config")
Dim nsmgr As New XmlNamespaceManager(xmlDoc.NameTable)
nsmgr.AddNamespace("d", "http://schemas.microsoft.com/.NetConfiguration/v2.0")
......
......
xmlDoc.SelectSingleNode("//d:appSettings", nsmgr).AppendChild(nodeRegion)
xmlDoc.Save("c:\inetpub\" & sServer & "\web.config")