XNode.ReadFrom Method (XmlReader)


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Creates an XNode from an XmlReader.

Namespace:   System.Xml.Linq
Assembly:  System.Xml.Linq (in System.Xml.Linq.dll)

Public Shared Function ReadFrom (
	reader As XmlReader
) As XNode


Type: System.Xml.XmlReader

An XmlReader positioned at the node to read into this XNode.

Return Value

Type: System.Xml.Linq.XNode

An XNode that contains the node and its descendant nodes that were read from the reader. The runtime type of the node is determined by the node type (NodeType) of the first node encountered in the reader.

Exception Condition

The XmlReader is not positioned on a recognized node type.


The underlying XmlReader throws an exception.

You can use this method to write a method that returns a collection of nodes, yielding each node as the node is read from the reader. This method enables you to process arbitrarily large XML files with a very small memory footprint.

The reader that you pass to this method might throw exceptions. ReadFrom does not catch all exceptions thrown by the reader; the unhandled exceptions bubble up to the code that called ReadFrom. In particular, your code should be prepared to handle XmlException.

For an example of how to stream a more complex document, see How to: Stream XML Fragments with Access to Header Information.

Certain standard query operators, such as OrderBy, iterate their source, collect all of the data, sort it, and then finally yield the first item in the sequence. If you use a query operator that materializes its source before yielding the first item, you will not retain a small memory footprint.

For an example of using LINQ to XML to transform extremely large XML documents while maintaining a small memory footprint, see How to: Perform Streaming Transform of Large XML Documents.

This example uses the following XML file, named Source.xml:

                <?xml version="1.0" encoding="utf-8" ?> 
  <Child Key="01">
  <Child Key="02">
  <Child Key="03">

This example creates a custom axis method that uses ReadFrom. You can query the custom axis by using a LINQ query.


The following example uses the yield return construct of C#. Because there is no equivalent feature in Visual Basic 2008, this example is provided only in C#.

                class Program
    static IEnumerable<XElement> StreamRootChildDoc(string uri)
        using (XmlReader reader = XmlReader.Create(uri))
            // Parse the file and display each of the nodes.
            while (reader.Read())
                switch (reader.NodeType)
                    case XmlNodeType.Element:
                        if (reader.Name == "Child")
                            XElement el = XElement.ReadFrom(reader) as XElement;
                            if (el != null)
                                yield return el;

    static void Main(string[] args)
        IEnumerable<string> grandChildData =
            from el in StreamRootChildDoc("Source.xml")
            where (int)el.Attribute("Key") > 1
            select (string)el.Element("GrandChild");

        foreach (string str in grandChildData)

This example produces the following output.


Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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