Change xml value using linq in c#

Question

I am working on this since the past 2 hours.I have an XML file which looks like this

<catalog>
  <captureInfo>
    <row>5</row>
    <col>5</col>
  </captureInfo>

  <patientInfo>
    <name>XYZ</name>
    <detail>details here</detail>
  </patientInfo>

  <imageData>
    <r0c0>
      <contrastFlag>true</contrastFlag>
    </r0c0>
  <imageData>
<catalog>

I want to change the value of contrastFlag. I tried this but its not working

XDocument xdoc = XDocument.Load(filename)
xdoc.Element("catalog")
                .Element("imageData")
                .Descendants()
                .Where(x => x.Value == "r0c0")
                .First()
                .SetElementValue("contrastFlag", "newValue");


            doc.Save("XMLFile1.xml");

Can I know where I am going wrong and what would be the correct approach?

i get this error - "System.NullReferenceException: Object reference not set to an instance of an object" — JustCurious
– JustCurious, Commented May 30, 2018 at 22:45
the <imageData> and <catalog> tags are not closed properly, but after that is fixed, this works for me xdoc.Element("catalog").Element("imageData").Element("r0c0").SetElementValue("contrastFlag", "newValue"); — Slai
– Slai, Commented May 30, 2018 at 23:04
From : .Where(x => x.Value == "r0c0") To: .Where(x => x.Name.LocalName == "r0c0") — jdweng
– jdweng, Commented May 31, 2018 at 0:20

Sach · Accepted Answer · 2018-05-30 23:29:30Z

1

It's not clear if you have multiple contrastFlag elements or not.

If there's only one, you can simply do this:

XDocument xdoc = XDocument.Load(filename);
var element = xdoc.Root.Descendants("contrastFlag").FirstOrDefault();
if (element != null)
    element.Value = "false";
xdoc.Save("sample1.xml");

If you have multiple elements, you can use XPath instead:

XDocument xdoc = XDocument.Load(filename);
var element = xdoc.Root.XPathSelectElement("//catalog//imageData//r0c0//contrastFlag");
if (element != null)
    element.Value = "false";
xdoc.Save("sample1.xml");

NOTE:

XPath is in using System.Xml.XPath namespace.

answered May 30, 2018 at 23:29

Sach

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Debashish Saha · Accepted Answer · 2018-05-30 23:05:10Z

0

.Where(x => x.Name == "r0c0")

Changed to this instead of x.Value because its an element Name.

answered May 30, 2018 at 23:05

Debashish Saha

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