Represents a reader that provides fast, non-cached, forward-only access to XML data.
Assembly: System.Xml (in System.Xml.dll)
provides forward-only, read-only access to a stream of XML data. The 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.
Although the Microsoft .NET Framework includes concrete implementations of the class, such as the XmlTextReader, XmlNodeReader, and the XmlValidatingReader classes, in the 2.0 release the recommended practice is to create instances using the Create method. For more information, see Creating XML Readers.
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.
For further discussion on the class, see Reading XML with the XmlReader.
The following items are things to consider when working with the class.
Exceptions thrown the 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 objects created by the Create method.
If you have DTD processing enabled, you can use the XmlSecureResolver to restrict the resources that the can access. You can also 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 include references to external resources such as a schema file. By default external resources are resolved using an XmlUrlResolver object with no user credentials. You can secure this further by doing one of the following:
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 , create a custom IStream implementation and supply it the .
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 , 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.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.