Average Rating: 5/5 | Rate this item | 4 users have rated this item.

Expertise: Beginner
Language: XML

June 14, 2004

Retrieve Specific Nodes When They Contain an xmlns Namespace Parameter

When an XML file contains a xmlns parameter, you can't use simple SelectSingleNode to retrieve a specific node. Take the following code, for example:

<?xml version="1.0" encoding="utf-8" ?> 
<OfferSheetXML xmlns="http://localhost/OfferSheetSchema.xsd" >
  <Offer>
    <OfferSheetId>31</OfferSheetId>
  </Offer>
</OfferSheetXML>

Now, try to run the following code with the above XML:

<%@ Import Namespace="System.Xml"%>
<%@ Page Language="C#" Debug="true"%>

<script runat="server">
void Page_Load(object sender, System.EventArgs e)
{
    XmlDocument xmlDoc = new XmlDocument();
    xmlDoc.Load(Server.MapPath("temp.xml"));

    XmlNode node = xmlDoc.SelectSingleNode("//OfferSheetXML");
    Response.Write ("Node Name : " + node.Name); 
}
</script>

Running the above code will generate the following error message:

System.NullReferenceException: Object reference not set to an instance of an object.
Line 16:  Response.Write ("Node Name : " + node.Name); 

The solution is to specifiy the namespace for the XPath. The following code solves the problem and retrieves the node:

<%@ Import Namespace="System.Xml"%>
<%@ Page Language="C#" Debug="true"%>

<script runat="server">
void Page_Load(object sender, System.EventArgs e)
{
    XmlDocument xmlDoc = new XmlDocument();
    xmlDoc.Load(Server.MapPath("temp.xml"));

    XmlNamespaceManager nsmRequest = new XmlNamespaceManager(xmlDoc.NameTable);
    nsmRequest.AddNamespace("ns1", "http://localhost/OfferSheetSchema.xsd");
    XmlNode node = xmlDoc.SelectSingleNode("//ns1:OfferSheetXML", nsmRequest);

    Response.Write ("Node Name : " + node.Name); 
}
</script>