How do I extract data from an XML file with Visual Basic?

Question

I've not used XML too much and I need a little help.

My .NET application gets this XML response from the W3C's public validation server:

<?xml version="1.0" encoding="UTF-8" ?> 
<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope">
    <env:Body>
        <m:markupvalidationresponse env:encodingStyle="http://www.w3.org/2003/05/soap-encoding" xmlns:m="http://www.w3.org/2005/10/markup-validator">
            <m:uri>upload://Form Submission</m:uri> 
            <m:checkedby>http://validator.w3.org/</m:checkedby> 
            <m:doctype>-//W3C//DTD XHTML 1.1//EN</m:doctype> 
            <m:charset>utf-8</m:charset> 
            <m:validity>true</m:validity> 
            <m:errors>
                <m:errorcount>0</m:errorcount> 
                <m:errorlist /> 
            </m:errors>
            <m:warnings>
                <m:warningcount>0</m:warningcount> 
                <m:warninglist /> 
            </m:warnings>
        </m:markupvalidationresponse>
    </env:Body>
</env:Envelope>

I want to extract from this the following values:

Uri as String
Checkedby as String
Doctype as String
CharSet as String
Validity as Boolean
ErrorList as System.Collections.Generic.List(Of W3CError)
WarningList as System.Collections.Generic.List(Of W3CError)

That type W3CError is a small class I created with the following properties:

Line as Integer
Col as Integer
Message as String
MessageId as String
Explanation as String
Source as String

Here's what I've go so far. But, this doesn't work...

Dim ResponseReader As Xml.XmlTextReader = New Xml.XmlTextReader(ResponseStream)
Dim ResponseDocument As New Xml.XPath.XPathDocument(ResponseReader)
Dim ResponseNavigator As Xml.XPath.XPathNavigator = ResponseDocument.CreateNavigator()
Dim ResponseIterator As Xml.XPath.XPathNodeIterator

'uri
ResponseIterator = ResponseNavigator.Select("uri")
ResponseIterator.MoveNext()
_Uri = ResponseIterator.Current.Value

'checked by
ResponseIterator = ResponseNavigator.Select("checkedby")
ResponseIterator.MoveNext()
_Checkedby = ResponseIterator.Current.Value

...etc...

How can I fix the broken code above? Or: Am I way off track with this? What's a better way?

do you have a WSDL available? VS should be able to generate classes for data types exposed by the web service for you automatically so you do not have to parse the SOAP output by hand. — Marek
– Marek, Commented Apr 8, 2010 at 5:12

Dude-Dastic · Accepted Answer · 2009-03-06 16:18:28Z

Try this

'Import these Namespaces at the top of your file
Imports System.Linq
Imports System.Xml.Linq
Imports <xmlns:env="http://www.w3.org/2003/05/soap-envelope">
Imports <xmlns:m="http://www.w3.org/2005/10/markup-validator">

'in a procedure do this
Dim doc As XDocument = <?xml version="1.0" encoding="UTF-8" ?> 
<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope">
    <env:Body>
        <m:markupvalidationresponse env:encodingStyle="http://www.w3.org/2003/05/soap-encoding" xmlns:m="http://www.w3.org/2005/10/markup-validator">
            <m:uri>upload://Form Submission</m:uri> 
            <m:checkedby>http://validator.w3.org/</m:checkedby> 
            <m:doctype>-//W3C//DTD XHTML 1.1//EN</m:doctype> 
            <m:charset>utf-8</m:charset> 
            <m:validity>true</m:validity> 
            <m:errors>
                <m:errorcount>0</m:errorcount> 
                <m:errorlist /> 
            </m:errors>
            <m:warnings>
                <m:warningcount>0</m:warningcount> 
                <m:warninglist /> 
            </m:warnings>
        </m:markupvalidationresponse>
    </env:Body>
</env:Envelope>

_Uri = doc.Root.<env:Body>.<m:markupvalidationresponse>.<m:uri>.Value
_Checkedby = doc.Root.<env:Body>.<m:markupvalidationresponse>.<m:checkedby>.Value
'note that the following code assumes you have a class named W3CError
_errorList = (From er in doc.Root...<m:errors> _
             Select New W3CError With {.Line = CInt(er.<m:line>.Value), .Col = CInt(er.<m:col>.Value), .Message = er.<m:message>.Value, .MessageId = er.<m:messageId>.Value, .Explanation = er.<m:explanation>.Value, .Source = er.<m:source>.Value}).ToList
'do the same for the _warningList as above
'now do what you want with it

Alex Reitbort · Accepted Answer · 2009-03-05 22:07:35Z

2

Have you heard about XPath?

XmlDocument doc  = new XmlDocument()
doc.Load(xml)
// set the namspace manager, I don't remember exact syntax
....
XmlNode node = doc.SelectSingleNode("//m:checkedby", namespaceManagerThatDeclaresMNamespace);

You code probably don't work because you are ignoring the namespaces in xml

answered Mar 5, 2009 at 22:07

Alex Reitbort

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Comments

Sruly · Accepted Answer · 2009-03-05 22:10:52Z

1

There is also linq2xml. It is located in System.Xml.Linq. It has a new XDocument class that is easier to work with than the older System.Xml.XmlDocument class.

answered Mar 5, 2009 at 22:10

Sruly

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