Introduction C # two ways to read XML

XML Functions

For XML, I think everyone knows it well. I don't need to bother to describe what it is. I think XML will surely shine in the future of Web development, XML is a scalable markup language that allows enterprises to develop their own data formats. For Internet data transmission, I think this is the most attractive place for our programmers!

Our topic today is not about the advantages of XML, but about how to use XML in C. Next, let's take a look at some basic theoretical knowledge about accessing XML using a program.

Two access models:

There are two models for accessing and then operating XML files in a program: DOM (Document Object Model) and stream model. The advantage of DOM is that it allows editing and updating XML documents, you can randomly access the data in the document and use XPath for query. However, the disadvantage of DOM is that it needs to load the entire document to the memory at a time. For large documents, this may cause resource problems. The stream model solves this problem well because it uses the stream concept to access XML files, that is, it only has the current node in the memory at any time, but it also has its shortcomings. It is read-only and only forward, and cannot perform backward navigation in the document. Although each has its own merits, we can also use the two in the program to complement each other.

I. DOM Document Object Model Operations

Copy codeThe Code is as follows: using System. Xml;

XmlDocument xml = new XmlDocument (); // Initialize an xml instance
Xml. Load (path); // import the specified xml file
Xml. Load (HttpContext. Current. Server. MapPath ("~ /File/bookstore. xml "); XmlNode root = xml. SelectSingleNode ("/root "); // specify a node
XmlNodeList childlist = root. ChildNodes; // retrieve all direct subnodes under a node
XmlNodeList nodelist = xml. selectNodes ("/Root/News"); // obtain the set of nodes with the same name as the string id = node. attributes ["id"]. value; // obtain the specified attribute Value of a specified Node
String content = node. InnerText; // get the text in the specified node
Root. HasChildNodes; // determines whether a subnode exists under the node.

1. attributes of the XmlDocument class

The attributes and descriptions of the XmlDocument class are shown in the following table.

Attribute	Description
Attributes	Attribute Set of the current node
BaseURI	Base URI of the current node
ChildNodes	All subnodes of a node
DocumentElement	Document Root
DocumentType	Nodes declared by DOCTYPE
FirstChild	The first subnode of the node.
HasChildNodes	Is there any subnode?
Implementation	Get the XmlImplementation object of the current document
InnerText	All text content contained in the node
InnerXml	All XML content contained by the node
IsReadOnly	Whether the current node is read-only
Item	Obtains the specified child element.
LastChild	Last subnode
LocalName	Obtain the local name of a node
Name	Get the node's qualified name
NamespaceURI	Get the namespace URI of the node
NameTable	Obtain the XmlNameTable associated with this implementation
NextSibling	Obtain the node that follows the node
NodeType	Obtains the type of the current node.
OuterXml	Obtain the flag indicating this node and all its subnodes
OwnerDocument	Obtains the XmlDocument to which the current node belongs.
ParentNode	Obtain the parent level of a node (for a node with a parent level)
Prefix	Get or set the namespace prefix of the node
PreserveWhitespace	Gets or sets a value that indicates whether to retain white space in the element content.
Previussibling	Obtain the node that follows the node
SchemaInfo	Returns the post-architecture verification information set (PSVI) of the node)
Schemas	Gets or sets the XmlSchemaSet object associated with this XmlDocument
Value	Obtains or sets the value of a node.
XmlResolver	Set XmlResolver for parsing external resources

2. methods of the XmlDocument class

The methods and descriptions of the XmlDocument class are shown in the following table.

Method	Description
AppendChild	Add the specified node to the end of the node's subnode list
CreateAttribute	Create an XmlAttribute with the specified name
CreateCDataSection	Create an XmlCDataSection containing the specified data
CreateComment	Create an XmlComment that contains the specified data
CreateDocumentFragment	Create XmlDocumentFragment
CreateDocumentType	Returns the new XmlDocumentType object.
CreateElement	Create XmlElement
CreateEntityReference	Create an XmlEntityReference with the specified name
CreateNavigator	Create a new XPathNavigator object used to navigate this document
CreateNode	Create XmlNode
CreateProcessingInstruction	Create an XmlProcessingInstruction with the specified name and Data
CreateSignificantWhitespace	Create an XmlSignificantWhitespace Node
CreateTextNode	Create XmlText with specified text
CreateWhitespace	Create an XmlWhitespace Node
CreateXmlDeclaration	Create an XmlDeclaration node with the specified value
GetElementById	Obtains the XmlElement with the specified ID.
GetElementsByTagName	Returns an XmlNodeList that contains a list of all elements that match the specified name.
GetNamespaceOfPrefix	Find the xmlns declaration closest to the given prefix within the current node range, and return the namespace URI in the Declaration
GetPrefixOfNamespace	Find the xmlns declaration closest to the specified namespace URI within the current node range, and return the prefix defined in the Declaration
GetType	Obtains the Type of the current instance.
ImportNode	Import a node from another document to the current document
InsertAfter	Insert the specified node to the referenced node.
InsertBefore	Insert the specified node to the specified referenced node.
Load	Load specified XML data
LoadXml	Load the XML document from the specified string
Normalize	Convert all XmlText nodes to "normal" Form
PrependChild	Add a specified node to the beginning of the node's subnode list
ReadNode	Create an XmlNode object based on the information in XmlReader. The reader must be located on a node or attribute.
RemoveAll	Removes all subnodes and/or attributes of the current node.
RemoveChild	Removes a specified subnode.
ReplaceChild	Replace Old nodes with new nodes
Save	Save the XML document to the specified location
SelectNodes	Select the node list that matches the XPath expression
SelectSingleNode	Select the first XmlNode that matches the XPath expression
Supports	Test whether DOM implements specific functions
Validate	Verify whether the XmlDocument is an XML Schema Definition Language (XSD) architecture contained in the Schemas attribute.
WriteContentTo	Saves all child levels of the XmlDocument node to the specified XmlWriter.
WriteTo	Saves the XmlDocument node to the specified XmlWriter

The following describes common methods.

(1) Load Method

This method can be used to import XML data from an XML file specified by a string, a stream object, a TextReader object, and an XmlReader object.

(2) LoadXml Method

This method imports XML data from a specific XML file. By default, the LoadXml method neither retains blank nor meaningful blank. This method does not perform DTD or architecture verification.

(3) Save Method

This method saves XML data to an XML file or a stream object, a TextReader object, and an XmlReader object to import XML data.

3. Events of the XmlDocument class

The events and descriptions of the XmlDocument class are shown in the following table.

Table events and descriptions of the XmlDocument class

Event	Description
NodeChanged	This occurs when the Value of the node that belongs to this document has been changed.
NodeChanging	This occurs when the Value of the node that belongs to this document is changed.
NodeInserted	This occurs when the node that belongs to this document has been inserted into another node.
NodeInserting	This occurs when the node that belongs to this document is inserted into another node.
NodeRemoved	This occurs when the node that belongs to this document has been removed from its parent.
NodeRemoving	This occurs when the node that belongs to this document is removed from the document.

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