New XML Features in .NET Version 2: Part I

 while (reader.MoveToNextSibling());

}

New methods aren t the only enhancements that have been added to the XmlReader class. It s also capable of performing validation in version 2. In version 1.1, an XmlValidatingReader had to be instantiated to validate XML against a DTD or XSD schema. In version 2, however, XmlReader can be used to parse and validate data. Validation is turned on by using XmlReaderSettings, a new class available in the framework.

XmlReaderSettings allows a variety of features to be set as a reader parses XML data. For example, white space, comments, and processing instructions can be ignored by setting to true the XmlReaderSettings IgnoreWhiteSpace, IgnoreComments, and IgnoreProcessingInstructions properties. By setting the CheckCharacters property to true, Character checking can be performed to ensure that only legal XML characters are used in the document. Validation can be performed by adding one or more schemas to the XmlReaderSettings Schemas collection and by setting the ValidationType property to ValidationType.Schema.

Once properties have been set on an XmlReaderSettings object it can be passed to the XmlReader s Create method. Figure 1 shows an example of using the XmlReaderSettings class, along with the XmlReader class, to validate an XML document against an XSD schema.

private bool status

public void btnSubmit_Click(object sender, EventArgs e) {

 string xmlPath = Server.MapPath("~/XML/MSDN.xml");

 string schemaPath = Server.MapPath("~/Schemas/MSDN.xsd");

 //Load schema used to validate

 XmlSchemaSet schemaSet = new XmlSchemaSet();

 schemaSet.Add(String.Empty, schemaPath);

 schemaSet.Compile();

 //Define XmlReader settings

 XmlReaderSettings readerSettings = new XmlReaderSettings();

 readerSettings.ValidationType = ValidationType.Schema;

 readerSettings.Schemas = schemaSet;

 //Hook up event handler to handle any validation errors

 readerSettings.ValidationEventHandler +=

   new ValidationEventHandler(ValidationEventHandler);

 //Create XmlReader instance and pass in XmlReaderSettings

 using (XmlReader reader =

   XmlReader.Create(xmlPath, readerSettings)) {

     while (reader.Read()) { }

 }

 this.lblOutput.Text =

(status) ? "Validation Succeeded!" : "Validation Failed!";

}

private void ValidationEventHandler(object sender,

 ValidationEventArgs e) {

  status = false;

}

Figure 1: The XmlReaderSettings class allows various XmlReader features to be turned on or off easily. This example demonstrates how to validate an XML document against an XSD schema that is loaded into the new XmlSchemaSet class.

What s New with XmlWriter?

The XmlReader class provides an efficient way to parse XML documents, but it can t be used to generate XML data. That s where .NET s XmlWriter class comes into play. XmlWriter allows XML data to be written to a variety of output sources, including Streams, TextWriters, files, and other XmlWriters.

Although the XmlWriter API hasn t changed as substantially as the XmlReader API in version 2, there are several changes that you can leverage to generate dynamic RSS feeds or other custom XML documents. One of the most important changes is in the way it is instantiated. In version 1.1, the following code would typically be written to generate XML:

XmlTextWriter writer = new XmlTextWriter(

 filePath,Encoding.UTF8);

writer.WriteStartElement("golfers");

 writer.WriteStartElement("golfer");

     writer.WriteAttributeString("name","Mike");

     writer.WriteAttributeString("handicap","14");

 writer.WriteEndElement();

writer.WriteEndElement();

writer.Close();

Version 1.1 contained an XmlWriter class, but it couldn t be instantiated using the new keyword because it was abstract. In version 2, the XmlWriter class is still abstract, but it now exposes a Create method that accepts a variety of parameters that control where the XML output goes:

//using keyword automatically closes the XmlWriter in C#

using (XmlWriter writer = XmlWriter.Create(path)) {

 writer.WriteStartElement("golfers");

     writer.WriteStartElement("golfer");

         writer.WriteAttributeString("name","Simon");

         writer.WriteAttributeString("handicap","2");

     writer.WriteEndElement();

 writer.WriteEndElement();

}

The XmlWriter s Create method can also accept an instance of a new class named XmlWriterSettings that can be used to apply indentation to XML output or cause attributes to be placed on separate lines. It can also be used to control the output encoding or prevent the XML declaration from being written out. Figure 2 demonstrates how the XmlWriterSettings class can be used. The output is shown in Figure 3.

XmlWriterSettings ws = new XmlWriterSettings();

ws.Indent = true;

ws.CheckCharacters = true;

ws.NewLineOnAttributes = true;

StringWriter sw = new StringWriter();

using (XmlWriter writer = XmlWriter.Create(sw, ws)) {

 writer.WriteStartElement("customers");

 writer.WriteStartElement("customer");

 writer.WriteAttributeString(

  "id", Guid.NewGuid().ToString());

 writer.WriteAttributeString("fname", "John");

 writer.WriteAttributeString("lname", "Doe");

 writer.WriteEndElement();

 writer.WriteStartElement("customer");

 writer.WriteAttributeString(

  "id", Guid.NewGuid().ToString());

 writer.WriteAttributeString("fname", "Jane");

 writer.WriteAttributeString("lname", "Doe");

 writer.WriteEndElement();

 writer.WriteEndElement(); //close customers

}

this.txtXml.Text = sw.GetStringBuilder().ToString();

Figure 2: The XmlWriterSettings class can be used to control several different features of XmlWriter. The code shown here uses XmlWriterSettings to ensure that valid XML characters are used, indentation is applied, and attributes are placed on their own line in the output.

  id="83ef3265-e94d-4587-ac00-faaee5ca4f03"

  fname="John"

  lname="Doe" />

  id="74be7621-632d-4f54-be1d-9f77a3ddf83b"

  fname="Jane"

  lname="Doe" />

Figure 3: XML output generated from running the code shown in Figure 2. Notice that each attribute is placed on its own line because the XmlWriterSettings NewLineOnAttributes property was set to true.

Displaying RSS Feeds with XmlReader and XmlWriter

Now that you ve seen a few of the new features associated with the XmlReader and XmlWriter classes in .NET version 2, let s finish up with an example of using these classes together to parse and display data from an RSS feed. Although several different options exist for parsing RSS feeds in the .NET Framework (XmlDataSource, DataSet, XPathNavigator, and others I ll discuss in Part II of this series), using the XmlReader and XmlWriter classes together provides a highly efficient and scalable solution because both work with streams of data.

To display an RSS feed, the XML data must first be parsed; the XmlReader class performs this job quite well. Each element within the RSS feed must be located so that the item s