How to read XML files using XmlReader in C # _c# tutorial

XmlReader provides us with a minimal resource-consuming way to parse XML data by reading the document forward and identifying the read elements. Most of the time we use XmlReader to validate the data validation of an XML file (using the Read () method of the XmlReader instance to read all the nodes sequentially to determine whether it matches the specified pattern). With this kind of non caching, read-only, forward-only way, a small amount of data is put into memory each time, and the memory footprint is small, which is the best choice for reading large XML files.

Let's take a look at the steps of the XmlReader class reading an XML file:

1, create an instance of the class using the Create () factory method of the XmlReader class, and pass the read XML filename as a parameter to the method;

2. Create a loop that calls the read () method repeatedly. This method starts at the first node of the file and reads all remaining nodes, but only one node is read per call. Returns true if one node can be read, and returns False when the end of the file is reached;

3. In this loop, the properties and methods of the XmlReader instance are checked to obtain information about the current node (type, name, data, and so on). Keep looping until read () returns false;

Let's look at an example:

Employees.xml file:

<?xml version= ' 1.0 '?>
<employees>
 <employee id= "1" > 
 <name>
 <firstname >Nancy</firstName>
 <lastName>Davolio</lastName> 
 </name>
 <city> seattle</city>
 <state>WA</state>
 <zipCode>98122</zipCode> 
 </ employee>
 <employee id= "2" > 
 <name>
 <firstName>Andrew</firstName>
 <lastName>Fuller</lastName>
 </name>
 <city>Tacoma</city>
 <state>WA</state>
 <zipCode>98401</zipCode> 
 </employee> 
</ Employees>

ASPX code:

<%@ Page language= "C #"%> <%@ Import namespace= ' system.xml '%> <script ' runat= ' server ' > void Page_Load (
 Object sender, EventArgs e) {//location of XML file string xmlfilepath = Server.MapPath ("~/employees.xml");
 try {using (XmlReader reader = Xmlreader.create (Xmlfilepath)) {string result; while (reader. Read ()) {//process Only the elements if reader.
 NodeType = = xmlnodetype.element) {result = ""; for (int count = 1; Count <= reader. Depth;
 count++) {result = = "= ="; result = = "=>" + reader.
 Name + "<br/>";
 Lblresult.text + = result; catch (Exception ex) {lblresult.text = "An Exception occurred:" + ex.
 message; } </script>  

Output results:

=> Employees
====> Employee
=======> Name
==========> FirstName
==========> LastName
=======> City
=======> State
=======> ZipCode
====> Employee
=======> Name
==========> FirstName
==========> LastName
=======> City
=======> State
=======> ZipCode

Let's look at the properties and methods of the XmlReader class:

Property	Description
Attributecount	Returns the number of properties for the current node
Depth	Returns the depth of the current node to determine whether the specified node has child nodes
Eof	To determine whether the reader is at the end of the stream
Hasattribute	Returns a Boolean value indicating whether the current node has an attribute
HasValue	Returns a Boolean value indicating whether the current node has a value
Isemptyelement	Determines whether the current node is an empty element
LocalName	Returns the local name of the current node
Name	Returns the qualified name of the current node
NamespaceURI	Returns the namespace URI of the current node
NodeType	Returns the node type of the current node as a XmlNodeType enumeration
Prefix	Returns the namespace prefix associated with the current node
ReadState	Returns the current state of the reader in the form of a ReadState enumeration
Settings	Returns the XmlReaderSettings object used to create the XmlReader instance
Value	Returns the value of the current node
ValueType	Get the CLR type of the current node

Important ways to XmlReader classes:

Method	Description
Close	Close the XmlReader object by setting the ReadState enumeration to Closed
Create	Creates an instance of the XmlReader object and returns it to the calling program
GetAttribute	Get the value of a property
Isstartelement	Indicates whether the current node is a start tag
MoveToAttribute	Move the reader to the specified property
MoveToContent	If the current node is not a content node, move the reader to the next content node
Movetoelement	Moves the reader to the element that contains the current property; To enumerate properties and to switch to elements that contain all of these properties
MoveToFirstAttribute	Move the reader to the first property of the current node
MoveToNextAttribute	Move the reader to the next property of the current node
Read	Reading the next node from the stream
ReadContentAs	Reading the contents of an object that provides a type
ReadElementContentAs	Reads the current element and returns the contents of the specified type object
Readendelement	Move reader over current end tag and move to next node
ReadInnerXml	Reads all contents of the current node, including markup, as a string
Readoutxml	Read the contents of a node, including the current node tag and child nodes
Readtodescendant	Move the reader to the next node that matches the descendant element
Readtofollowing	Keep reading until you find the specified element
Readtonextslibing	Move the reader to the next node that matches the sibling element
Readvaluechunk	Allows reading of large text streams embedded in XML documents

XmlNodeType members of the enumeration:

Members	Description
Attribute	Property
Cdata	CDATA Region
Comment	XML annotations
Document	Document object that represents the root of the XML tree
DocumentFragment	Document fragment
DocumentType	Document Type declaration
Element,endelement	Start element and end element
Entity,endentity	Start entity declaration and end Entity declaration
EntityReference	Entity references (such as <)
None	There is no read node and query node type use
notation	Symbol entries in the DTD
ProcessingInstruction	XML processing Instructions
SignificantWhitespace	White space in a mixed content model document, or when Xml:space=preserve is set up using the
Text	The textual content of the element
Whitespace	whitespace between tags
XmlDeclaration	XML declaration at the top of the document

Important attributes of the XmlReaderSettings class:

Property	Description
Checkcharacters	Allows you to get or set a value that indicates whether the character check is performed
ConformanceLevel	To obtain or set the XmlReader object's compliance requirements
Ignorecomment	Allows you to get or set a value that indicates whether the annotation is ignored
IgnoreprocessinginstructIon	Specifies whether to ignore processing instructions
Ignorewhitespace	Specify whether to ignore meaningless spaces
ProhibitDTD	Specifies whether DTD processing is allowed
Schemas	Specifies the XmlSchemaSet to use when performing XML validation
Validationflags	Gets or sets the value used to specify the mode validation settings
ValidationType	Gets or sets a value that specifies the type of validation to be performed
XmlResolver	Set up a xmlreslover for accessing external documents

With the XmlReaderSettings class, you can specify a series of features supported by the XmlReader object, so simply pass xmlreadersettings as a parameter into the XmlReader create () method. As shown below:

 <script runat= "server" > void Page_Load (object sender, EventArgs e) {string x 
 Mlfilepath = Server.MapPath ("~/employees.xml"); Create the XmlReaderSettings object and set appropriate properties xmlreadersettings settings = new XmlReaderSettings ()
 ; Settings.
 Ignorecomments = true; Settings.
 Ignorewhitespace = true; try {//get reference to the XmlReader object using (XmlReader reader = xmlreader.create (Xmlfilepath, Settings)) {St
 Ring result; while (reader. Read ()) {//process Only the elements if reader.
 NodeType = = xmlnodetype.element) {//reset The variable for a new Element result = ""; for (int count = 1; Count <= reader. Depth;
 count++) {result = = "= ="; result = = "=>" + reader.
 Name + "<br/>";
 Lblresult.text + = result; catch (Exception ex) {lblresult.text = "An Exception occurred:" + ex.
 message; } </script> 

In summary, we can use the XmlReader class to read XML files in a non cached, read-only, forward-only way, which takes up less memory and is recommended for everyone to use.