How to read the xmlelement with specific attribute name

Question

3.00/5 (1 vote)

See more:

Hi i have the xml similar to below
and each xml can have multiple IRO nodes under IRP node.

<irp>

<irn n="name1">

now i am trying to get the value of "s" attribute which is in "T" element and will load in to collection, but i nned to get the attribute s value only for the names matching to IRO. n attribute

XML

<pre lang="XML"><?xml version="1.0" encoding="UTF-8"?>

-<IR>


-<IRP comprised="True" n="EFPLANT-SC-2">


-<IRO n="U1-ABV -13820ACT" cd="Schema document version">


-<P i="True" dn="Construction status 2" pd="ConstructionStatus2">

<T v="Recalibrate" s="LastIn"/>

<T v="Recalibrate" s="ELE"/>

<T v="New" s="IIC"/>

<T v="New" s="PID"/>

</P>


-<P i="True" dn="Construction status" pd="ConstructionStatus">

<T v="Existing" s="LastIn"/>

<T v="Existing" s="ELE"/>

<T v="New" s="IIC"/>

<T v="New" s="PID"/>

</P>


-<P i="False" dn="Instrument sequence in loop" pd="InstSequenceInLoop">

<T v="0" s="LastIn"/>

<T v="0" s="ELE"/>

<T v="0" s="IIC"/>

</P>


-<P i="False" dn="X-coincidence factor" pd="XCoincidenceFactor">

<T v="0" s="LastIn"/>

<T v="0" s="ELE"/>

</P>


-<P i="False" dn="Y-coincidence factor" pd="YCoincidenceFactor">

<T v="0" s="LastIn"/>

<T v="0" s="ELE"/>

</P>

What I have tried:

Private Function ProcessFileToKnowToolsWhichHavePropPublishedInDomain(ByVal pstrPath As String, ByVal pstrname As String) As List(Of String)

Dim lcolDomainwhichhaveatleastoneproperty As New List(Of String)
Dim lvalidateDOMReply As New XmlDocument
lvalidateDOMReply.Load(pstrPath)
Dim xml As XElement = XElement.Load(pstrPath)
'Dim userNodes As XmlNodeList = lvalidateDOMReply.SelectNodes("IR/IRP/IRO[@n=" + pstrname + "]")
Dim myNodes As IEnumerable(Of XElement) = xml.Descendants("IRP").Descendants("IRO").Where(Function(x) x.Attribute("n").Value = pstrname)
'lvalidateDOMReply.

For Each lobjPropertyNode As XElement In myNodes
Dim tool As String = (lobjPropertyNode.Elements("s").Value).ToString()
If Not lcolDomainwhichhaveatleastoneproperty.Contains(tool) Then lcolDomainwhichhaveatleastoneproperty.Add(tool)
Next

Return lcolDomainwhichhaveatleastoneproperty
End Function

i HAVE TRIED ABOVE CODE but getting the object refernce exception.not able to find wher ethe value is nothing please suggest

Posted 8-Jun-16 6:56am

Member 12573064

Updated 8-Jun-16 9:07am

Add a Solution

Comments

Sergey Alexandrovich Kryukov 8-Jun-16 14:02pm

System.Xml.Linq.XDocument is more suitable for such things, as it supports LINQ to XML.
As to the exception, just use the debugger. You did not even comment the line where the exception is thrown...
—SA

Member 12573064 8-Jun-16 14:14pm

Hi SA,
Thanks for the reply
It has thrown the exception in the for each loop at
Dim Tool As string

2 solutions

Solution 2

Please see my comment to the question. Better use System.Xml.Linq.XDocument more suitable for such things as it supports LINQ to XML:
XDocument Class (System.Xml.Linq),
LINQ to XML.

Member 12573064 wrote:

It has thrown the exception in the for each loop at
Dim Tool As string

As to your exception, it looks like you have a real stopper here. Look at this line:

VB

Dim tool As String = (lobjPropertyNode.Elements("s").Value).ToString()

If you are sure that this is the line where the exception is thrown, it can be only if lobjPropertyNode.Elements("s") returns null, and then you try to dereference this object, assuming it is not null, by taking its member .Value. At this point, the exception is thrown.

And then you probably do wrong thing. Instead of inspecting the expressions under the debugger, you start guessing and asking questions which you should answer, not anyone else. You cannot do it when you face such situations; it's very important to learn dealing with them all by yourself.

Not to worry. This is one of the easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferences by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object".

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx,
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx.

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx.

Good luck,

—SA

Posted 8-Jun-16 9:07am

Sergey Alexandrovich Kryukov

Comments

Richard Deeming 8-Jun-16 15:25pm

Based on the code in the question, he's already using XLinq. It's slightly confused by the fact that he's loading the XML twice - once into an XmlDocument and once into an XElement - but the loop is using the XElement.

Sergey Alexandrovich Kryukov 8-Jun-16 17:09pm

Yes, it is confusing. Why System.XML.XmlDocument? My point is different: I suggested to use System.Xml.Linq.XDocument instead of System.XML.XmlDocument.
—SA

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Richard Deeming · Accepted Answer · 2016-06-08T09:05:00

You are selecting the matching IRO nodes, and then trying to read the element "s" from those nodes. Based on the XML you've posted, the IRO nodes do not have a child element called "s".

If you want to read the attribute from the T elements, you need to select those elements, and read the attribute:

VB.NET

Dim myNodes As IEnumerable(Of XElement) = xml
    .Elements("IRP")
    .Elements("IRO")
    .Where(Function(x) x.Attribute("n").Value = pstrname)
    .Elements("P")
    .Elements("T")

For Each lobjPropertyNode As XElement In myNodes
    Dim tool As String = lobjPropertyNode.Attribute("s").Value
    ...
Next