Question

I come from a vb6 background. New to .net and new to xml. I am trying to retrieve nodes from an xml file. I have found several methods used (xmltextreader/serialization, xmldocument, xpath) I’m using xpath simply because I got some results with it first 🙂 My problem I am sure is namespace related but all examples I’ve found are much simpler than the xml I have. Here is part of the xml I need to access and a snippet of my code.

<?xml version="1.0" encoding="utf-8"?>
<MTConnectStreams xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:mtconnect.org:MTConnectStreams:1.2 http://mtconnect.org/schemas/MTConnectStreams_1.2.xsd" xmlns="urn:mtconnect.org:MTConnectStreams:1.2">
  <Header creationTime="2012-11-29T12:30:19Z" instanceId="2" nextSequence="1918272" sender="Tarus MTConnect Instance" bufferSize="5000" firstSequence="1913272" lastSequence="1918271" version="1.2" />
  <Streams>
    <DeviceStream name="Vertical Bridge" uuid="TPIVB1">
      <ComponentStream component="Device" name="Vert" componentId="TPIVert">
        <Events>
          <Availability dataItemId="avail" timestamp="2012-11-27T23:19:40Z" sequence="44">AVAILABLE</Availability>
        </Events>
      </ComponentStream>
      <ComponentStream component="Linear" name="X" componentId="X">
        <Samples>
          <AxisFeedrate dataItemId="xs1" timestamp="2012-11-29T12:29:54Z" sequence="1717806" name="x_feed_cmd" subType="COMMANDED" units="MILLIMETER/SECOND">0</AxisFeedrate>

Trying to retrieve AxisFeedrate I have this:

Dim xDoc As XPathDocument = New XPathDocument(sUrl)
Dim xNav As XPathNavigator = xDoc.CreateNavigator
Dim xIt As XPathNodeIterator = xNav.Select("//AxisFeedrate")
Dim i As Integer

For i = 1 To xIt.Count
    xIt.MoveNext()
    msgbox (xIt.Current.Value)

If I change the root node to simply ‘MTConnectStreams’ everything works. Following namespace examples online I made the following changes to my code. But I still get zero results back when restoring the original root node.

Dim nsMgr = New XmlNamespaceManager(xNav.NameTable)
nsMgr.AddNamespace("ns", "http://www.w3.org/2001/XMLSchema-instance")
Dim xIt As XPathNodeIterator = xNav.Select("//ns:AxisFeedrate", nsMgr)

Can someone help me get past this hurdle?

Answer 1

Your root node declares that the default namespace is “urn:mtconnect.org:MTConnectStreams:1.2”, so you need to use that:

Dim nsMgr = New XmlNamespaceManager(xNav.NameTable)
nsMgr.AddNamespace("mt", "urn:mtconnect.org:MTConnectStreams:1.2")
Dim xIt As XPathNodeIterator = xNav.Select("//mt:AxisFeedrate", nsMgr)