XElement Class Overview

Artigo
07/05/2012

The XElement class is one of the fundamental classes in LINQ to XML. It represents an XML element. You can use this class to create elements; change the content of the element; add, change, or delete child elements; add attributes to an element; or serialize the contents of an element in text form. You can also interoperate with other classes in System.Xml, such as XmlReader, XmlWriter, and XslCompiledTransform.

XElement Functionality

This topic describes the functionality provided by the XElement class.

Constructing XML Trees

You can construct XML trees in a variety of ways, including the following:

You can construct an XML tree in code. For more information, see Creating XML Trees.
You can parse XML from various sources, including a TextReader, text files, or a Web address (URL). For more information, see Parsing XML.
You can use an XmlReader to populate the tree. For more information, see ReadFrom.
If you have a module that can write content to an XmlWriter, you can use the CreateWriter method to create a writer, pass the writer to the module, and then use the content that is written to the XmlWriter to populate the XML tree.

However, the most common way to create an XML tree is as follows:

XElement contacts =
    new XElement("Contacts",
        new XElement("Contact",
            new XElement("Name", "Patrick Hines"), 
            new XElement("Phone", "206-555-0144"),
            new XElement("Address",
                new XElement("Street1", "123 Main St"),
                new XElement("City", "Mercer Island"),
                new XElement("State", "WA"),
                new XElement("Postal", "68042")
            )
        )
    );

Dim contacts As XElement = _
    <Contacts>
        <Contact>
            <Name>Patrick Hines</Name>
            <Phone>206-555-0144</Phone>
            <Address>
                <Street1>123 Main St</Street1>
                <City>Mercer Island</City>
                <State>WA</State>
                <Postal>68042</Postal>
            </Address>
        </Contact>
    </Contacts>

Another very common technique for creating an XML tree involves using the results of a LINQ query to populate an XML tree, as shown in the following example:

XElement srcTree = new XElement("Root",
    new XElement("Element", 1),
    new XElement("Element", 2),
    new XElement("Element", 3),
    new XElement("Element", 4),
    new XElement("Element", 5)
);
XElement xmlTree = new XElement("Root",
    new XElement("Child", 1),
    new XElement("Child", 2),
    from el in srcTree.Elements()
    where (int)el > 2
    select el
);
Console.WriteLine(xmlTree);

Dim srcTree As XElement = _
    <Root>
        <Element>1</Element>
        <Element>2</Element>
        <Element>3</Element>
        <Element>4</Element>
        <Element>5</Element>
    </Root>
Dim xmlTree As XElement = _
    <Root>
        <Child>1</Child>
        <Child>2</Child>
        <%= From el In srcTree.Elements() _
            Where el.Value > 2 _
            Select el %>
    </Root>
Console.WriteLine(xmlTree)

This example produces the following output:

<Root>
  <Child>1</Child>
  <Child>2</Child>
  <Element>3</Element>
  <Element>4</Element>
  <Element>5</Element>
</Root>

Serializing XML Trees

You can serialize the XML tree to a File, a TextWriter, or an XmlWriter.

For more information, see Serializing XML Trees.

Retrieving XML Data via Axis Methods

You can use axis methods to retrieve attributes, child elements, descendant elements, and ancestor elements. LINQ queries operate on axis methods, and provide several flexible and powerful ways to navigate through and process an XML tree.

For more information, see LINQ to XML Axes.

Querying XML Trees

You can write LINQ queries that extract data from an XML tree.

For more information, see Querying XML Trees.

Modifying XML Trees

You can modify an element in a variety of ways, including changing its content or attributes. You can also remove an element from its parent.

For more information, see Modifying XML Trees (LINQ to XML).

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