Using Xpath With Default Namespace in C#

Question

I\'ve got an XML document with a default namespace. I\'m using a XPathNavigator to select a set of nodes using Xpath as follows:

XmlElement myXML = ...;           


        

Answer 1

I encountered a similar problem with a blank default namespace. In this example XML, I have a mix of elements with namespace prefixes, and a single element (DataBlock) without:

 
  
   7
  
  
   Value
   
   
    Value
   
  
 

I attempted to use an XPath that worked in XPath Visualizer, but did not work in my code:

  XmlDocument doc = new XmlDocument();
  doc.Load( textBox1.Text );
  XPathNavigator nav = doc.DocumentElement.CreateNavigator();
  XmlNamespaceManager nsman = new XmlNamespaceManager( nav.NameTable );
  foreach ( KeyValuePair nskvp in nav.GetNamespacesInScope( XmlNamespaceScope.All ) ) {
    nsman.AddNamespace( nskvp.Key, nskvp.Value );
  }

  XPathNodeIterator nodes;

  XPathExpression failingexpr = XPathExpression.Compile( "/src:SRCExample/DataBlock/a:DocID/a:IdID" );
  failingexpr.SetContext( nsman );
  nodes = nav.Select( failingexpr );
  while ( nodes.MoveNext() ) {
    string testvalue = nodes.Current.Value;
  }

I narrowed it down to the "DataBlock" element of the XPath, but couldn't make it work except by simply wildcarding the DataBlock element:

  XPathExpression workingexpr = XPathExpression.Compile( "/src:SRCExample/*/a:DocID/a:IdID" );
  failingexpr.SetContext( nsman );
  nodes = nav.Select( failingexpr );
  while ( nodes.MoveNext() ) {
    string testvalue = nodes.Current.Value;
  }

After much headscratching and googling (which landed me here) I decided to tackle the default namespace directly in my XmlNamespaceManager loader by changing it to:

  foreach ( KeyValuePair nskvp in nav.GetNamespacesInScope( XmlNamespaceScope.All ) ) {
    nsman.AddNamespace( nskvp.Key, nskvp.Value );
    if ( nskvp.Key == "" ) {
      nsman.AddNamespace( "default", nskvp.Value );
    }
  }

So now "default" and "" point to the same namespace. Once I did this, the XPath "/src:SRCExample/default:DataBlock/a:DocID/a:IdID" returned my results just like I wanted. Hopefully this helps to clarify the issue for others.