XmlReader Class
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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
'Declaration
<DefaultMemberAttribute("Item")> _
Public MustInherit Class XmlReader _
Implements IDisposable
[DefaultMemberAttribute("Item")]
public abstract class XmlReader : IDisposable
The XmlReader type exposes the following members.
Properties
| Name | Description | |
|---|---|---|
.gif "Public property") .gif "Supported by Silverlight for Windows Phone") .gif "Supported by Xbox 360") |
AttributeCount | When overridden in a derived class, gets the number of attributes on the current node. |
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BaseURI | When overridden in a derived class, gets the base URI of the current node. |
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CanReadBinaryContent | Gets a value indicating whether the XmlReader implements the binary content read methods. |
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CanReadValueChunk | Gets a value indicating whether the XmlReader implements the ReadValueChunk method. |
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CanResolveEntity | Gets a value indicating whether this reader can parse and resolve entities. |
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Depth | When overridden in a derived class, gets the depth of the current node in the XML document. |
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EOF | When overridden in a derived class, gets a value indicating whether the reader is positioned at the end of the stream. |
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HasAttributes | Gets a value indicating whether the current node has any attributes. |
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HasValue | When overridden in a derived class, gets a value indicating whether the current node can have a Value. |
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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. |
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IsEmptyElement | When overridden in a derived class, gets a value indicating whether the current node is an empty element (for example, <MyElement/>). |
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Item[Int32] | When overridden in a derived class, gets the value of the attribute with the specified index. |
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Item[String] | When overridden in a derived class, gets the value of the attribute with the specified Name. |
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Item[String, String] | When overridden in a derived class, gets the value of the attribute with the specified LocalName and NamespaceURI. |
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LocalName | When overridden in a derived class, gets the local name of the current node. |
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Name | When overridden in a derived class, gets the qualified name of the current node. |
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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. |
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NameTable | When overridden in a derived class, gets the XmlNameTable associated with this implementation. |
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NodeType | When overridden in a derived class, gets the type of the current node. |
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Prefix | When overridden in a derived class, gets the namespace prefix associated with the current node. |
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ReadState | When overridden in a derived class, gets the state of the reader. |
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Settings | Gets the XmlReaderSettings object used to create this XmlReader instance. |
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Value | When overridden in a derived class, gets the text value of the current node. |
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ValueType | Gets the common language runtime (CLR) type for the current node. |
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XmlLang | When overridden in a derived class, gets the current xml:lang scope. |
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XmlSpace | When overridden in a derived class, gets the current xml:space scope. |
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Methods
| Name | Description | |
|---|---|---|
.gif "Public method") |
Close | When overridden in a derived class, changes the ReadState to Closed. |
.gif "Static member") |
Create(Stream) | Creates a new XmlReader instance using the specified stream. |
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Create(String) | Creates a new XmlReader instance with specified URI. |
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Create(TextReader) | Creates a new XmlReader instance with the specified TextReader. |
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Create(Stream, XmlReaderSettings) | Creates a new XmlReader instance with the specified stream and XmlReaderSettings object. |
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Create(String, XmlReaderSettings) | Creates a new instance with the specified URI and XmlReaderSettings. |
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Create(TextReader, XmlReaderSettings) | Creates a new XmlReader instance using the specified TextReader and XmlReaderSettings objects. |
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Create(XmlReader, XmlReaderSettings) | Creates a new XmlReader instance with the specified XmlReader and XmlReaderSettings objects. |
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Create(Stream, XmlReaderSettings, String) | Creates a new XmlReader instance using the specified stream, base URI, and XmlReaderSettings object. |
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Create(Stream, XmlReaderSettings, XmlParserContext) | Creates a new XmlReader instance using the specified stream, XmlReaderSettings, and XmlParserContext objects. |
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Create(String, XmlReaderSettings, XmlParserContext) | Creates a new XmlReader instance using the specified URI, XmlReaderSettings, and XmlParserContext objects. |
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Create(TextReader, XmlReaderSettings, String) | Creates a new XmlReader instance using the specified TextReader, XmlReaderSettings, and base URI. |
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Create(TextReader, XmlReaderSettings, XmlParserContext) | Creates a new XmlReader instance using the specified TextReader, XmlReaderSettings, and XmlParserContext objects. |
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Dispose() | |
.gif "Protected method") |
Dispose(Boolean) | Releases the unmanaged resources used by the XmlReader and optionally releases the managed resources. |
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Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
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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.) |
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GetAttribute(Int32) | When overridden in a derived class, gets the value of the attribute with the specified index. |
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GetAttribute(String) | When overridden in a derived class, gets the value of the attribute with the specified Name. |
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GetAttribute(String, String) | When overridden in a derived class, gets the value of the attribute with the specified LocalName and NamespaceURI. |
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GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
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GetType | Gets the Type of the current instance. (Inherited from Object.) |
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IsName | Gets a value indicating whether the string argument is a valid XML name. |
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IsNameToken | Gets a value indicating whether or not the string argument is a valid XML name token. |
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IsStartElement() | Calls MoveToContent and tests if the current content node is a start tag or empty element tag. |
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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. |
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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. |
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LookupNamespace | When overridden in a derived class, resolves a namespace prefix in the current element's scope. |
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MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
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MoveToAttribute(Int32) | When overridden in a derived class, moves to the attribute with the specified index. |
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MoveToAttribute(String) | When overridden in a derived class, moves to the attribute with the specified Name. |
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MoveToAttribute(String, String) | When overridden in a derived class, moves to the attribute with the specified LocalName and NamespaceURI. |
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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. |
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MoveToElement | When overridden in a derived class, moves to the element that contains the current attribute node. |
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MoveToFirstAttribute | When overridden in a derived class, moves to the first attribute. |
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MoveToNextAttribute | When overridden in a derived class, moves to the next attribute. |
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Read | When overridden in a derived class, reads the next node from the stream. |
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ReadAttributeValue | When overridden in a derived class, parses the attribute value into one or more Text, EntityReference, or EndEntity nodes. |
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ReadContentAs | Reads the content as an object of the type specified. |
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ReadContentAsBase64 | Reads the content and returns the Base64 decoded binary bytes. |
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ReadContentAsBinHex | Reads the content and returns the BinHex decoded binary bytes. |
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ReadContentAsBoolean | Reads the text content at the current position as a Boolean. |
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ReadContentAsDateTime | Reads the text content at the current position as a DateTime object. |
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ReadContentAsDecimal | Reads the text content at the current position as a Decimal object. |
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ReadContentAsDouble | Reads the text content at the current position as a double-precision floating-point number. |
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ReadContentAsFloat | Reads the text content at the current position as a single-precision floating point number. |
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ReadContentAsInt | Reads the text content at the current position as a 32-bit signed integer. |
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ReadContentAsLong | Reads the text content at the current position as a 64-bit signed integer. |
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ReadContentAsObject | Reads the text content at the current position as an Object. |
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ReadContentAsString | Reads the text content at the current position as a String object. |
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ReadElementContentAs(Type, IXmlNamespaceResolver) | Reads the element content as the requested type. |
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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. |
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ReadElementContentAsBase64 | Reads the element and decodes the Base64 content. |
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ReadElementContentAsBinHex | Reads the element and decodes the BinHex content. |
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ReadElementContentAsBoolean() | Reads the current element and returns the contents as a Boolean object. |
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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. |
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ReadElementContentAsDateTime() | Reads the current element and returns the contents as a DateTime object. |
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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. |
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ReadElementContentAsDecimal() | Reads the current element and returns the contents as a Decimal object. |
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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. |
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ReadElementContentAsDouble() | Reads the current element and returns the contents as a double-precision floating-point number. |
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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. |
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ReadElementContentAsFloat() | Reads the current element and returns the contents as single-precision floating-point number. |
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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. |
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ReadElementContentAsInt() | Reads the current element and returns the contents as a 32-bit signed integer. |
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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. |
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ReadElementContentAsLong() | Reads the current element and returns the contents as a 64-bit signed integer. |
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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. |
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ReadElementContentAsObject() | Reads the current element and returns the contents as an Object. |
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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. |
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ReadElementContentAsString() | Reads the current element and returns the contents as a String object. |
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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. |
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ReadEndElement | Checks that the current content node is an end tag and advances the reader to the next node. |
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ReadInnerXml | When overridden in a derived class, reads all the content, including markup, as a string. |
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ReadOuterXml | When overridden in a derived class, reads the content, including markup, representing this node and all its children. |
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ReadStartElement() | Checks that the current node is an element and advances the reader to the next node. |
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ReadStartElement(String) | Checks that the current content node is an element with the given Name and advances the reader to the next node. |
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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. |
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ReadSubtree | Returns a new XmlReader instance that can be used to read the current node, and all its descendants. |
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ReadToDescendant(String) | Advances the XmlReader to the next descendant element with the specified qualified name. |
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ReadToDescendant(String, String) | Advances the XmlReader to the next descendant element with the specified local name and namespace URI. |
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ReadToFollowing(String) | Reads until an element with the specified qualified name is found. |
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ReadToFollowing(String, String) | Reads until an element with the specified local name and namespace URI is found. |
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ReadToNextSibling(String) | Advances the XmlReader to the next sibling element with the specified qualified name. |
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ReadToNextSibling(String, String) | Advances the XmlReader to the next sibling element with the specified local name and namespace URI. |
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ReadValueChunk | Reads large streams of text embedded in an XML document. |
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ResolveEntity | When overridden in a derived class, resolves the entity reference for EntityReference nodes. |
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Skip | Skips the children of the current node. |
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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.
.gif "Important note") Important Note: |
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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.
Platform Notes
.png "Silverlight for Windows Phone"){kind=icon}
Silverlight for 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
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
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