CODEWITHSUNDEEP
xmlvb.net
Adam
Adam

Reputation: 6122

Selecting node value in XML document returns null

This is the XML response I'm trying to parse:

<?xml version="1.0" encoding="utf-8"?>
<double xmlns="http://www.webserviceX.NET/">0.7627</double>

The VB code:

Dim responseString As String

Dim fromCurrency As String = "EUR"
Dim toCurrency As String = "USD"


Dim req As System.Net.HttpWebRequest = System.Net.HttpWebRequest.Create("http://www.webservicex.net/CurrencyConvertor.asmx/ConversionRate?FromCurrency=" & fromCurrency & "&ToCurrency=" & toCurrency)
Dim Resp As System.Net.HttpWebResponse = req.GetResponse()
Dim reader As StreamReader = New StreamReader(Resp.GetResponseStream)
responseString = reader.ReadToEnd()

'get the XML
Dim objXML As New XmlDocument
objXML.LoadXml(responseString)

Dim root As XmlNode = objXML.DocumentElement

Dim nodeList As XmlNodeList = root.SelectNodes("/double")

How can I read the result value of "0.7627"?

I tried:

nodeList(0).InnerText

and 

nodeList(0).SelectSingleNode("/double").InnerText

Both throw the error "Object reference not set to an instance of an object."

I also tried adding a namespace manager:

Dim mgr As XmlNamespaceManager = New XmlNamespaceManager(objXML.NameTable)
mgr.AddNamespace("currency", objXML.DocumentElement.NamespaceURI)

Dim node As XmlNode = objXML.SelectSingleNode("double", mgr)

And select via:

node.InnerText

But that also throws "Object reference not set to an instance of an object."

Upvotes: 2

Views: 2897

Answers (2)

MarcinJuraszek
MarcinJuraszek

Reputation: 125620

You can try using LINQ to XML:

Imports System.XML.Linq

(...)

Dim req As System.Net.HttpWebRequest = System.Net.HttpWebRequest.Create("http://www.webservicex.net/CurrencyConvertor.asmx/ConversionRate?FromCurrency=" & fromCurrency & "&ToCurrency=" & toCurrency)
Dim Resp As System.Net.HttpWebResponse = req.GetResponse()

Dim doc as XDocument = XDocument.Load(Resp.GetResponseStream)
Dim myDoubleValue as Double = CDbl(doc.Root)

myDoubleValue should be 0.7627

Upvotes: 0

Cristian Lupascu
Cristian Lupascu

Reputation: 40526

Here are the problems I see with the code:

  • you need to correctly define the namespace (it's the one in the XML: "http://www.webserviceX.NET/")

  • you need to use the namespace in the XPath expression you pass to SelectSingleNode

Here's how I did it (using C#):

var namespaceManager = new XmlNamespaceManager(objXML.NameTable);
namespaceManager.AddNamespace("wsx", "http://www.webserviceX.NET/");

var doubleNode = root.SelectSingleNode("/wsx:double", namespaceManager);

Console.WriteLine(doubleNode.InnerText);

Here's the VB.NET equivalent (I hope it's right, I converted the code using a tool):

Dim namespaceManager = New XmlNamespaceManager(objXML.NameTable)
namespaceManager.AddNamespace("wsx", "http://www.webserviceX.NET/")

Dim doubleNode = root.SelectSingleNode("/wsx:double", namespaceManager)

Console.WriteLine(doubleNode.InnerText)

Upvotes: 3

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