Validation Using a Wrapped XmlReader Object

You can create a new XmlReader object that is wrapped around another XmlReader object. This allows you to add additional features on top of another XmlReader object. For example, the XmlNodeReader class does not support data validation. By creating an XmlReader object that wraps around the XmlNodeReader object, you can validate the data stored in the XmlNodeReader object.

Example

In the following example, an XML file is loaded into an XML document and modified. The XML document is passed to an XmlNodeReader, which is then passed to the XmlReader.Create method. When the validating reader parses the file, it can validate any changes made to the XML file.

Imports System
Imports System.Xml
Imports System.Xml.Schema
Imports System.IO

public class Sample 

  public shared sub Main() 

    ' Create and load the XML document. 
    Dim doc as XmlDocument = new XmlDocument()
    doc.Load("booksSchema.xml")

    ' Make changes to the document. 
    Dim book as XmlElement
    book = CType(doc.DocumentElement.FirstChild, XmlElement)
    book.SetAttribute("publisher", "Worldwide Publishing")

    ' Create an XmlNodeReader using the XML document. 
    Dim nodeReader as XmlNodeReader = new XmlNodeReader(doc)

    ' Set the validation settings on the XmlReaderSettings object. 
    Dim settings as XmlReaderSettings = new XmlReaderSettings()
    settings.ValidationType = ValidationType.Schema
    settings.Schemas.Add("urn:bookstore-schema", "books.xsd")
    AddHandler settings.ValidationEventHandler, AddressOf ValidationCallBack

    ' Create a validating reader that wraps the XmlNodeReader object. 
    Dim reader as XmlReader = XmlReader.Create(nodeReader,settings)

    ' Parse the XML file.
    while (reader.Read())
    end while
  end sub

  ' Display any validation errors.
  private shared sub ValidationCallBack(sender as object, e as ValidationEventArgs)
    Console.WriteLine("Validation Error: {0}", e.Message)
  end sub

end class

using System;
using System.Xml;
using System.Xml.Schema;
using System.IO;

public class Sample {

  public static void Main() {

    // Create and load the XML document.
    XmlDocument doc = new XmlDocument();
    doc.Load("booksSchema.xml");

    // Make changes to the document.
    XmlElement book = (XmlElement) doc.DocumentElement.FirstChild;
    book.SetAttribute("publisher", "Worldwide Publishing");

    // Create an XmlNodeReader using the XML document.
    XmlNodeReader nodeReader = new XmlNodeReader(doc);

    // Set the validation settings on the XmlReaderSettings object.
    XmlReaderSettings settings = new XmlReaderSettings();
    settings.ValidationType = ValidationType.Schema;
    settings.Schemas.Add("urn:bookstore-schema", "books.xsd");
    settings.ValidationEventHandler += new ValidationEventHandler (ValidationCallBack);

   // Create a validating reader that wraps the XmlNodeReader object.
   XmlReader reader = XmlReader.Create(nodeReader, settings);

   // Parse the XML file. 
   while (reader.Read());
  }

  // Display any validation errors. 
  private static void ValidationCallBack(object sender, ValidationEventArgs e) {
    Console.WriteLine("Validation Error: {0}", e.Message);
  }
}

Input

The following files are used as input.

bookSchema.xml

<?xml version='1.0'?>
<bookstore xmlns="urn:bookstore-schema">
  <book genre="autobiography">
    <title>The Autobiography of Benjamin Franklin</title>
    <author>
      <first-name>Benjamin</first-name>
      <last-name>Franklin</last-name>
    </author>
    <price>8.99</price>
  </book>
  <book genre="novel">
    <title>The Confidence Man</title>
    <author>
      <first-name>Herman</first-name>
      <last-name>Melville</last-name>
    </author>
    <price>11.99</price>
  </book>
</bookstore>

books.xsd

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns="urn:bookstore-schema"
    elementFormDefault="qualified"
    targetNamespace="urn:bookstore-schema">

 <xsd:element name="bookstore" type="bookstoreType"/>

 <xsd:complexType name="bookstoreType">
  <xsd:sequence maxOccurs="unbounded">
   <xsd:element name="book"  type="bookType"/>
  </xsd:sequence>
 </xsd:complexType>

 <xsd:complexType name="bookType">
  <xsd:sequence>
   <xsd:element name="title" type="xsd:string"/>
   <xsd:element name="author" type="authorName"/>
   <xsd:element name="price"  type="xsd:decimal"/>
  </xsd:sequence>
  <xsd:attribute name="genre" type="xsd:string"/>
 </xsd:complexType>

 <xsd:complexType name="authorName">
  <xsd:sequence>
   <xsd:element name="first-name"  type="xsd:string"/>
   <xsd:element name="last-name" type="xsd:string"/>
  </xsd:sequence>
 </xsd:complexType>

</xsd:schema>

Output

Validation Error: The 'publisher' attribute is not declared.

See Also

Concepts

Reading XML with the XmlReader

Other Resources

Validating XML Data with XmlReader