How to set attribute value for existing XML element

Question

I have an existing XML file and I would like to update some of its attributes. I googled and see many similar questions and answers but I have no luck.

<?xml version="1.0"?>
<system ExportDate="2/15/2018" ExportTime="11:56 AM EST" DateFormat="MM/dd/yyyy" NumberFormat="HH:mm:ss " SchemaValidation="true" ExportVersion="2016.1.SP1710.57 [Build 82] - 27 September 2017 (01:30 IST)" xmlns="http://www.mentor.com/harness/Schema/LibrarySchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.mentor.com/harness/Schema/LibrarySchema file:/C:/MentorGraphics/VeSys_Client/dtd/LibrarySchema.xsd" XMLVersion="1.6">
  <librarymaterial librarymaterial_id="XXX" description="YYY" materialcode="ZZZ" />
 </system>

I am trying to set new values for some of the attributes.
For the root, I have no issue

xmlDoc.DocumentElement.SetAttribute("ExportDate", DateTime.Now.ToShortDateString());
xmlDoc.DocumentElement.SetAttribute("ExportTime", DateTime.Now.ToShortTimeString() + " EST");

However, when I try the different methods but no hope

Method 1:

XmlNode node = xmlDoc.SelectSingleNode("/system/librarymaterial");
node.Attributes["librarymaterial_id"].Value=_librarymaterial_id;

Error:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

node was null.

Method 2:

var nodes = xmlDoc.SelectNodes("/system/librarymaterial");
foreach (XmlElement n in nodes)
{
    n.SetAttribute("librarymaterial_id", _librarymaterial_id);
}

This does not create an error, but the librarymaterial_id does not get updated.

Note that `system` has a namespace. You need a namespace manager — Thomas Weller, Feb 15 '18 at 17:14
@ThomasWeller thanks for correcting me. I deleted my comment. — FaizanHussainRabbani, Feb 15 '18 at 17:18
As @ThomasWeller pointed out, you'll require a namespace manager to do so, kindly go through this answer: https://stackoverflow.com/a/1089210/4222487 — FaizanHussainRabbani, Feb 15 '18 at 17:19

Saket Choubey · Accepted Answer · 2018-02-16T05:05:53.387

2

        XmlNodeList dataNodes = doc.GetElementsByTagName("librarymaterial");

        for (int i = 0; i < dataNodes.Count; i++)
        {
            XmlAttribute attr = dataNodes[i].Attributes["librarymaterial_id"];
            attr.Value = "USA";
        }

Try this code.

edited Feb 16 '18 at 05:05

answered Feb 15 '18 at 17:31

Saket Choubey

916
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it works so there are at least 2 solutions to the problem. Thanks! – Secret Feb 15 '18 at 17:38
Once you have list of nodes in a variable, you can play around with it. Hence there can be multiple solutions to the same problem. Thanks! – Saket Choubey Feb 15 '18 at 17:48
Nooooo! Why loop through all nodes and then modify the first one n times? – Thomas Weller Feb 15 '18 at 20:24
Typeo, please check now – Saket Choubey Feb 16 '18 at 05:06

How to set attribute value for existing XML element

1 Answers1