Reading and Writing XML Documents in .NET
XML provides platform independent, self-descriptive and
very flexible way to represent your data. .NET has harnessed the capabilities
of XML in variety of ways. In addition to providing W3C compatible
classes .NET also provides additional classes which make
XML document manipulation easy. In this article we will take a look at reading and
writing XML documents using .NET specific classes.
To access the content of an XML document you need to parse the document and
reach to the specific parts of it. The software which allows you to do that is
called as XML parser.
The parsers are of two types:
DOM parsers : These parsers built a tree of XML document in memory
and allow navigation to various nodes and attributes.
SAX parsers : These parsers process XML document in sequential fashion.
They have low memory footprint than DOM parsers.
In MSXML Ver.3, Microsoft has provided both of the parsers for our use. In
.NET we have DOM parser matching closely with existing MSXML parser. The SAX
parser has undergone some variation but provides similar functionality.
The pre-.NET parser i.e. MSXML provided classes and interfaces closely
matching W3C recommendations. .NET also follows the same tradition but adds many
easy to use and flexible ways to manipulate XML documents.
XML and .NET
XML related classes are available in System.XML namespace. In this article we
will primarily discuss about .NET specific classes for reading and writing XML
To read XML documents System.XML provides a class called
XmlTextReader. This class is derived from XmlReader and provides easy access to
various parts of XML document. This class can be thought as forward-only and
read only cursor.
To write XML documents System.XML provides a class called XmlTextWriter. This
class is derived from XmlWriter and allows quick writing of XML documents.
The methods provided by these classes are very easy to
use and self explaining as compared to W3C DOM . This is mainly because these
classes allow various methods to be called directly on themselves. They provide
'current node' for you to manipulate as opposed to W3C DOM classes where you
have to track individual nodes. These classes do not require some thing like mydoc.ChildNodes(0).ChildNodes(1).... to access
various attributes or content of the node. (You will see examples of using XmlTextReader
and XmlTextWriter in later sections)
Using XmlTextReader Class
Now, we will see how to use XmlTextReader class.
e.g. In VB.NET
e.g. In VB.NET
dim reader as XmlTextReader
reader = new XmlTextReader ("c:\xml\books.xml")
e.g. In VB.NET
do while (reader.Read())
'do some action here
The Read() method returns true if the node is successfully read else returns
false. If node is successfully read, you can use properties and methods on the
node to perform tasks like checking node type, access attributes, access content
of node etc. You can call these methods directly on reader object.
Following table lists important properties of XmlTextReader class.
||This method advances the 'cursor' to the next
node. Returns true if node is read successfully. You can use this method
in a While loop to process the document.|
||This property returns the type of node i.e.
Element, text node etc. The type is one from XmlNodeType
||This property returns name of the current
||This property returns the content of the node.|
||These Readxxxx() kind of properties return content of node as a
specific data type as opposed to value property.|
||This method returns string value of given
||This boolean property indicates whether the node
has any attributes.|
Using XmlTextWriter Class
Now, let us see how to use XmlTextWriter Class.
e.g. In VB.NET
dim writer as xmltextwriter
The second argument of the constructor indicates the
encoding to be used. The value of null indicates default encoding (ASCII)
Now we can write various parts of XML document into the
file. You will be calling various methods on the instance of XmlTextWriter class
directly. Following table lists important methods of XmlTextWriter Class.
||This method writes XML processing instruction to
the document i.e. <?xml version="1.0" ?>|
||This method writes start tag of an element to the
||This method is called after calling
WriteStartElement() and inserts corresponding end tag in the document|
||This method is nested with WriteStartElement()
and WriteEndElement() methods and writes an attribute to the element|
||This method creates a text only elements|
||This method flushes document buffer to disk. It is helpful if your
document is too big.|
||This method closes the XML document stream.|