XmlReader Class

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Represents a reader that provides fast, non-cached, forward-only access to XML data.

Inheritance Hierarchy

System..::.Object
System.Xml..::.XmlReader
System.Xml..::.XmlDictionaryReader

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

Syntax

Public MustInherit Class XmlReader _
    Implements IDisposable
public abstract class XmlReader : IDisposable

The XmlReader type exposes the following members.

Constructors

Name Description
XmlReader Initializes a new instance of the XmlReader class.

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Properties

Name Description
AttributeCount When overridden in a derived class, gets the number of attributes on the current node.
BaseURI When overridden in a derived class, gets the base URI of the current node.
CanReadBinaryContent Gets a value indicating whether the XmlReader implements the binary content read methods.
CanReadValueChunk Gets a value indicating whether the XmlReader implements the ReadValueChunk method.
CanResolveEntity Gets a value indicating whether this reader can parse and resolve entities.
Depth When overridden in a derived class, gets the depth of the current node in the XML document.
EOF When overridden in a derived class, gets a value indicating whether the reader is positioned at the end of the stream.
HasAttributes Gets a value indicating whether the current node has any attributes.
HasValue When overridden in a derived class, gets a value indicating whether the current node can have a Value.
IsDefault When overridden in a derived class, gets a value indicating whether the current node is an attribute that was generated from the default value defined in the DTD.
IsEmptyElement When overridden in a derived class, gets a value indicating whether the current node is an empty element (for example, <MyElement/>).
Item[([(Int32])]) When overridden in a derived class, gets the value of the attribute with the specified index.
Item[([(String])]) When overridden in a derived class, gets the value of the attribute with the specified Name.
Item[([(String, String])]) When overridden in a derived class, gets the value of the attribute with the specified LocalName and NamespaceURI.
LocalName When overridden in a derived class, gets the local name of the current node.
Name When overridden in a derived class, gets the qualified name of the current node.
NamespaceURI When overridden in a derived class, gets the namespace URI (as defined in the W3C Namespace specification) of the node on which the reader is positioned.
NameTable When overridden in a derived class, gets the XmlNameTable associated with this implementation.
NodeType When overridden in a derived class, gets the type of the current node.
Prefix When overridden in a derived class, gets the namespace prefix associated with the current node.
ReadState When overridden in a derived class, gets the state of the reader.
Settings Gets the XmlReaderSettings object used to create this XmlReader instance.
Value When overridden in a derived class, gets the text value of the current node.
ValueType Gets the common language runtime (CLR) type for the current node.
XmlLang When overridden in a derived class, gets the current xml:lang scope.
XmlSpace When overridden in a derived class, gets the current xml:space scope.

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Methods

Name Description
Close When overridden in a derived class, changes the ReadState to Closed.
Create(Stream) Creates a new XmlReader instance using the specified stream.
Create(String) Creates a new XmlReader instance with specified URI.
Create(TextReader) Creates a new XmlReader instance with the specified TextReader.
Create(Stream, XmlReaderSettings) Creates a new XmlReader instance with the specified stream and XmlReaderSettings object.
Create(String, XmlReaderSettings) Creates a new instance with the specified URI and XmlReaderSettings.
Create(TextReader, XmlReaderSettings) Creates a new XmlReader instance using the specified TextReader and XmlReaderSettings objects.
Create(XmlReader, XmlReaderSettings) Creates a new XmlReader instance with the specified XmlReader and XmlReaderSettings objects.
Create(Stream, XmlReaderSettings, String) Creates a new XmlReader instance using the specified stream, base URI, and XmlReaderSettings object.
Create(Stream, XmlReaderSettings, XmlParserContext) Creates a new XmlReader instance using the specified stream, XmlReaderSettings, and XmlParserContext objects.
Create(String, XmlReaderSettings, XmlParserContext) Creates a new XmlReader instance using the specified URI, XmlReaderSettings, and XmlParserContext objects.
Create(TextReader, XmlReaderSettings, String) Creates a new XmlReader instance using the specified TextReader, XmlReaderSettings, and base URI.
Create(TextReader, XmlReaderSettings, XmlParserContext) Creates a new XmlReader instance using the specified TextReader, XmlReaderSettings, and XmlParserContext objects.
Dispose()()() Releases all resources used by the current instance of the XmlReader class.
Dispose(Boolean) Releases the unmanaged resources used by the XmlReader and optionally releases the managed resources.
Equals(Object) Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Finalize Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
GetAttribute(Int32) When overridden in a derived class, gets the value of the attribute with the specified index.
GetAttribute(String) When overridden in a derived class, gets the value of the attribute with the specified Name.
GetAttribute(String, String) When overridden in a derived class, gets the value of the attribute with the specified LocalName and NamespaceURI.
GetHashCode Serves as a hash function for a particular type. (Inherited from Object.)
GetType Gets the Type of the current instance. (Inherited from Object.)
GetValueAsync Asynchronously gets the value of the current node.
IsName Gets a value indicating whether the string argument is a valid XML name.
IsNameToken Gets a value indicating whether or not the string argument is a valid XML name token.
IsStartElement()()() Calls MoveToContent and tests if the current content node is a start tag or empty element tag.
IsStartElement(String) Calls MoveToContent and tests if the current content node is a start tag or empty element tag and if the Name property of the element found matches the given argument.
IsStartElement(String, String) Calls MoveToContent and tests if the current content node is a start tag or empty element tag and if the LocalName and NamespaceURI properties of the element found match the given strings.
LookupNamespace When overridden in a derived class, resolves a namespace prefix in the current element's scope.
MemberwiseClone Creates a shallow copy of the current Object. (Inherited from Object.)
MoveToAttribute(Int32) When overridden in a derived class, moves to the attribute with the specified index.
MoveToAttribute(String) When overridden in a derived class, moves to the attribute with the specified Name.
MoveToAttribute(String, String) When overridden in a derived class, moves to the attribute with the specified LocalName and NamespaceURI.
MoveToContent Checks whether the current node is a content (non-white space text, CDATA, Element, EndElement, EntityReference, or EndEntity) node. If the node is not a content node, the reader skips ahead to the next content node or end of file. It skips over nodes of the following type: ProcessingInstruction, DocumentType, Comment, Whitespace, or SignificantWhitespace.
MoveToContentAsync Asynchronously checks whether the current node is a content node. If the node is not a content node, the reader skips ahead to the next content node or end of file.
MoveToElement When overridden in a derived class, moves to the element that contains the current attribute node.
MoveToFirstAttribute When overridden in a derived class, moves to the first attribute.
MoveToNextAttribute When overridden in a derived class, moves to the next attribute.
Read When overridden in a derived class, reads the next node from the stream.
ReadAsync Asynchronously reads the next node from the stream.
ReadAttributeValue When overridden in a derived class, parses the attribute value into one or more Text, EntityReference, or EndEntity nodes.
ReadContentAs Reads the content as an object of the type specified.
ReadContentAsAsync Asynchronously reads the content as an object of the type specified.
ReadContentAsBase64 Reads the content and returns the Base64 decoded binary bytes.
ReadContentAsBase64Async Asynchronously reads the content and returns the Base64 decoded binary bytes.
ReadContentAsBinHex Reads the content and returns the BinHex decoded binary bytes.
ReadContentAsBinHexAsync Asynchronously reads the content and returns the BinHex decoded binary bytes.
ReadContentAsBoolean Reads the text content at the current position as a Boolean.
ReadContentAsDateTime Reads the text content at the current position as a DateTime object.
ReadContentAsDateTimeOffset Reads the text content at the current position as a DateTimeOffset object.
ReadContentAsDecimal Reads the text content at the current position as a Decimal object.
ReadContentAsDouble Reads the text content at the current position as a double-precision floating-point number.
ReadContentAsFloat Reads the text content at the current position as a single-precision floating point number.
ReadContentAsInt Reads the text content at the current position as a 32-bit signed integer.
ReadContentAsLong Reads the text content at the current position as a 64-bit signed integer.
ReadContentAsObject Reads the text content at the current position as an Object.
ReadContentAsObjectAsync Asynchronously reads the text content at the current position as an Object.
ReadContentAsString Reads the text content at the current position as a String object.
ReadContentAsStringAsync Asynchronously reads the text content at the current position as a String object.
ReadElementContentAs(Type, IXmlNamespaceResolver) Reads the element content as the requested type.
ReadElementContentAs(Type, IXmlNamespaceResolver, String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the element content as the requested type.
ReadElementContentAsAsync Asynchronously reads the element content as the requested type.
ReadElementContentAsBase64 Reads the element and decodes the Base64 content.
ReadElementContentAsBase64Async Asynchronously reads the element and decodes the Base64 content.
ReadElementContentAsBinHex Reads the element and decodes the BinHex content.
ReadElementContentAsBinHexAsync Asynchronously reads the element and decodes the BinHex content.
ReadElementContentAsBoolean()()() Reads the current element and returns the contents as a Boolean object.
ReadElementContentAsBoolean(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as a Boolean object.
ReadElementContentAsDateTime()()() Reads the current element and returns the contents as a DateTime object.
ReadElementContentAsDateTime(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as a DateTime object.
ReadElementContentAsDecimal()()() Reads the current element and returns the contents as a Decimal object.
ReadElementContentAsDecimal(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as a Decimal object.
ReadElementContentAsDouble()()() Reads the current element and returns the contents as a double-precision floating-point number.
ReadElementContentAsDouble(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as a double-precision floating-point number.
ReadElementContentAsFloat()()() Reads the current element and returns the contents as single-precision floating-point number.
ReadElementContentAsFloat(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as a single-precision floating-point number.
ReadElementContentAsInt()()() Reads the current element and returns the contents as a 32-bit signed integer.
ReadElementContentAsInt(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as a 32-bit signed integer.
ReadElementContentAsLong()()() Reads the current element and returns the contents as a 64-bit signed integer.
ReadElementContentAsLong(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as a 64-bit signed integer.
ReadElementContentAsObject()()() Reads the current element and returns the contents as an Object.
ReadElementContentAsObject(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as an Object.
ReadElementContentAsObjectAsync Asynchronously reads the current element and returns the contents as an Object.
ReadElementContentAsString()()() Reads the current element and returns the contents as a String object.
ReadElementContentAsString(String, String) Checks that the specified local name and namespace URI matches that of the current element, then reads the current element and returns the contents as a String object.
ReadElementContentAsStringAsync Asynchronously reads the current element and returns the contents as a String object.
ReadEndElement Checks that the current content node is an end tag and advances the reader to the next node.
ReadInnerXml When overridden in a derived class, reads all the content, including markup, as a string.
ReadInnerXmlAsync Asynchronously reads all the content, including markup, as a string.
ReadOuterXml When overridden in a derived class, reads the content, including markup, representing this node and all its children.
ReadOuterXmlAsync Asynchronously reads the content, including markup, representing this node and all its children.
ReadStartElement()()() Checks that the current node is an element and advances the reader to the next node.
ReadStartElement(String) Checks that the current content node is an element with the given Name and advances the reader to the next node.
ReadStartElement(String, String) Checks that the current content node is an element with the given LocalName and NamespaceURI and advances the reader to the next node.
ReadSubtree Returns a new XmlReader instance that can be used to read the current node, and all its descendants.
ReadToDescendant(String) Advances the XmlReader to the next descendant element with the specified qualified name.
ReadToDescendant(String, String) Advances the XmlReader to the next descendant element with the specified local name and namespace URI.
ReadToFollowing(String) Reads until an element with the specified qualified name is found.
ReadToFollowing(String, String) Reads until an element with the specified local name and namespace URI is found.
ReadToNextSibling(String) Advances the XmlReader to the next sibling element with the specified qualified name.
ReadToNextSibling(String, String) Advances the XmlReader to the next sibling element with the specified local name and namespace URI.
ReadValueChunk Reads large streams of text embedded in an XML document.
ReadValueChunkAsync Asynchronously reads large streams of text embedded in an XML document.
ResolveEntity When overridden in a derived class, resolves the entity reference for EntityReference nodes.
Skip Skips the children of the current node.
SkipAsync Asynchronously skips the children of the current node.
ToString Returns a string that represents the current object. (Inherited from Object.)

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Remarks

XmlReader provides forward-only, read-only access to a stream of XML data. The XmlReader class conforms to the W3C Extensible Markup Language (XML) 1.0 and the Namespaces in XML recommendations.

The current node refers to the node on which the reader is positioned. The reader is advanced using any of the read methods and properties reflect the value of the current node.

Important Note:

You must use Create method to create XmlReader instances.

XmlReader throws an XmlException on XML parse errors. After an exception is thrown the state of the reader is not predictable. For example, the reported node type may be different than the actual node type of the current node. Use the ReadState property to check whether the reader is in error state.

Security Considerations

The following items are things to consider when working with the XmlReader class.

  • Exceptions thrown the XmlReader can disclose path information that you do not want bubbled up to the application. Your applications must catch exceptions and process them appropriately.

  • Do not enable DTD processing if you are concerned about denial of service issues or if you are dealing with untrusted sources. DTD processing is disabled by default for XmlReader objects created by the Create method.

    You can design your application so that the XML processing is memory and time constrained. For example, configure time-out limits in your ASP.NET application.

  • XML data can contain a large number of attributes, namespace declarations, nested elements and so on that require a substantial amount of time to process. To limit the size of the input that is sent to the XmlReader, create a custom IStream implementation and supply it the XmlReader.

  • The ReadValueChunk method can be used to handle large streams of data. This method reads a small number of characters at a time instead of allocating a single string for the whole value.

  • When reading an XML document with a large number of unique local names, namespaces, or prefixes, a problem can occur. If you are using class that derives from XmlReader, and you call either the LocalName, Prefix, or NamespaceURI property for each item, the returned string is added to a NameTable. The collection held by the NameTable never decreases in size, creating a virtual "memory leak" of the string handles. One mitigation for this is to derive from the NameTable class and enforce a maximum size quota. (There is no way to prevent the use of a NameTable, or to switch the NameTable when it is full). Another mitigation is to avoid using the properties mentioned and instead use the MoveToAttribute method with the IsStartElement method where possible; those methods do not return strings and thus avoid the problem of overfilling the NameTable collection.

Version Notes

Windows Phone

XmlReader does not fail when numeric character entity computation overflows. Instead, an empty string is returned to Value.

Examples

The following example navigates through the stream to determine the current node type, and then uses XmlWriter to output the XmlReader content.

Dim output As StringBuilder = New StringBuilder()

Dim xmlString As String = "<?xml version='1.0'?>" & _
                "<!-- This is a sample XML document -->" & _
                "<Items>" & _
                  "<Item>test with a child element <more/> stuff</Item>" & _
                "</Items>"
' Create an XmlReader
Using reader As XmlReader = XmlReader.Create(New StringReader(xmlString))
    Dim ws As XmlWriterSettings = New XmlWriterSettings()
    ws.Indent = True
    Using writer As XmlWriter = XmlWriter.Create(output, ws)

        ' Parse the file and display each of the nodes.
        While reader.Read()
            Select Case reader.NodeType
                Case XmlNodeType.Element
                    writer.WriteStartElement(reader.Name)
                Case XmlNodeType.Text
                    writer.WriteString(reader.Value)
                Case XmlNodeType.XmlDeclaration
                Case XmlNodeType.ProcessingInstruction
                    writer.WriteProcessingInstruction(reader.Name, reader.Value)
                Case XmlNodeType.Comment
                    writer.WriteComment(reader.Value)
                Case XmlNodeType.EndElement
                    writer.WriteFullEndElement()
            End Select
        End While
    End Using
End Using
OutputTextBlock.Text = output.ToString()
StringBuilder output = new StringBuilder();

String xmlString =
        @"<?xml version='1.0'?>
        <!-- This is a sample XML document -->
        <Items>
          <Item>test with a child element <more/> stuff</Item>
        </Items>";
// Create an XmlReader
using (XmlReader reader = XmlReader.Create(new StringReader(xmlString)))
{
    XmlWriterSettings ws = new XmlWriterSettings();
    ws.Indent = true;
    using (XmlWriter writer = XmlWriter.Create(output, ws))
    {

        // Parse the file and display each of the nodes.
        while (reader.Read())
        {
            switch (reader.NodeType)
            {
                case XmlNodeType.Element:
                    writer.WriteStartElement(reader.Name);
                    break;
                case XmlNodeType.Text:
                    writer.WriteString(reader.Value);
                    break;
                case XmlNodeType.XmlDeclaration:
                case XmlNodeType.ProcessingInstruction:
                    writer.WriteProcessingInstruction(reader.Name, reader.Value);
                    break;
                case XmlNodeType.Comment:
                    writer.WriteComment(reader.Value);
                    break;
                case XmlNodeType.EndElement:
                    writer.WriteFullEndElement();
                    break;
            }
        }

    }
}
OutputTextBlock.Text = output.ToString();

Version Information

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Platforms

Windows Phone

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

See Also

Reference

System.Xml Namespace