Question

I have a xml file . I have to search for an attribute and to replace its value with some value using c#
Further i dont know how many times does this attribute come and in how many elements as this xml is generated dynamically.
Any help over this?

Answer 1

One way is to load the document into a System.Xml.XmlDocument instance, then find all occurrences of the respective attribute by using the SelectNodes method of the XmlDocument instance with an XPath expression and modify them accordingly.

Here’s an example:

Assume the following Xml document:

<?xml version="1.0"?>
<test>
    <a/>
    <b myAttribute="someValue"/>
    <c myAttribute="someOtherValue"/>
    <d/>
    <e>
        <f myAttribute="yetAnotherValue" anotherAttribute="anIrrelevantValue"/>
    </e>
</test>

Save the Xml document as test.xml. In the same directory, compile the following program. It will change the values of all attributes that are called myAttribute (selected by the XPath expression //@myAttribute):

using System;
using System.Xml;

class Program
{
    public static void Main(string[] args)
    {
        XmlDocument doc = new XmlDocument();
        doc.Load("test.xml");

        Console.WriteLine("Before:");
        Console.WriteLine(doc.OuterXml);

        foreach (XmlNode node in doc.SelectNodes("//@myAttribute")) {
            node.Value = "new value";
        }

        Console.WriteLine("After:");
        Console.WriteLine(doc.OuterXml);

        doc.Save("test.xml");

        Console.ReadLine();
    }
}

(For your convenience, it also outputs the Xml document before and after the modification.)

With Namespaces

Now, the example is extended with namespaces (the XLink one, as requested by the OP):

Xml file:

<?xml version="1.0"?>
<test xmlns:xlink="http://www.w3.org/1999/xlink">
    <a/>
    <b xlink:myAttribute="someValue"/>
    <c myAttribute="someOtherValue"/>
    <d/>
    <e>
        <f xlink:myAttribute="yetAnotherValue" anotherAttribute="anIrrelevantValue"/>
    </e>
</test>

C# code:

using System;
using System.Xml;

class Program
{
    public static void Main(string[] args)
    {
        XmlDocument doc = new XmlDocument();
        doc.Load("test.xml");

        Console.WriteLine("Before:");
        Console.WriteLine(doc.OuterXml);

        XmlNamespaceManager nsMgr = new XmlNamespaceManager(doc.NameTable);
        nsMgr.AddNamespace("xlink", "http://www.w3.org/1999/xlink");
        foreach (XmlNode node in doc.SelectNodes("//@xlink:myAttribute", nsMgr)) {
            node.Value = "new value";
        }

        Console.WriteLine("After:");
        Console.WriteLine(doc.OuterXml);

        doc.Save("test.xml");

        Console.ReadLine();
    }
}

Remark 1: Note how only two occurrences of attributes called myAttribute are modified now, the third one (in the <c> element) does not belong to the namespace indicated in the XPath expression.

Remark 2: The namespace prefix used in the Xml file and the C# code happens to be the same (xlink), but this is not required. You could, for example, use xl in the C# code instead and obtain the same result (only showing the changed lines):

nsMgr.AddNamespace("xl", "http://www.w3.org/1999/xlink");
foreach (XmlNode node in doc.SelectNodes("//@xl:myAttribute", nsMgr)) {