Validating an XML against referenced XSD in C#

You need to create an XmlReaderSettings instance and pass that to your XmlReader when you create it. Then you can subscribe to the ValidationEventHandler in the settings to receive validation errors. Your code will end up looking like this:

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

public class ValidXSD
{
    public static void Main()
    {

        // Set the validation settings.
        XmlReaderSettings settings = new XmlReaderSettings();
        settings.ValidationType = ValidationType.Schema;
        settings.ValidationFlags |= XmlSchemaValidationFlags.ProcessInlineSchema;
        settings.ValidationFlags |= XmlSchemaValidationFlags.ProcessSchemaLocation;
        settings.ValidationFlags |= XmlSchemaValidationFlags.ReportValidationWarnings;
        settings.ValidationEventHandler += new ValidationEventHandler(ValidationCallBack);

        // Create the XmlReader object.
        XmlReader reader = XmlReader.Create("inlineSchema.xml", settings);

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

    }
    // Display any warnings or errors.
    private static void ValidationCallBack(object sender, ValidationEventArgs args)
    {
        if (args.Severity == XmlSeverityType.Warning)
            Console.WriteLine("\tWarning: Matching schema not found.  No validation occurred." + args.Message);
        else
            Console.WriteLine("\tValidation error: " + args.Message);

    }
}

A simpler way, if you are using .NET 3.5, is to use XDocument and XmlSchemaSet validation.

XmlSchemaSet schemas = new XmlSchemaSet();
schemas.Add(schemaNamespace, schemaFileName);

XDocument doc = XDocument.Load(filename);
string msg = "";
doc.Validate(schemas, (o, e) => {
    msg += e.Message + Environment.NewLine;
});
Console.WriteLine(msg == "" ? "Document is valid" : "Document invalid: " + msg);

See the MSDN documentation for more assistance.

The following example validates an XML file and generates the appropriate error or warning.

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

public class Sample
{

    public static void Main()
    {
        //Load the XmlSchemaSet.
        XmlSchemaSet schemaSet = new XmlSchemaSet();
        schemaSet.Add("urn:bookstore-schema", "books.xsd");

        //Validate the file using the schema stored in the schema set.
        //Any elements belonging to the namespace "urn:cd-schema" generate
        //a warning because there is no schema matching that namespace.
        Validate("store.xml", schemaSet);
        Console.ReadLine();
    }

    private static void Validate(String filename, XmlSchemaSet schemaSet)
    {
        Console.WriteLine();
        Console.WriteLine("\r\nValidating XML file {0}...", filename.ToString());

        XmlSchema compiledSchema = null;

        foreach (XmlSchema schema in schemaSet.Schemas())
        {
            compiledSchema = schema;
        }

        XmlReaderSettings settings = new XmlReaderSettings();
        settings.Schemas.Add(compiledSchema);
        settings.ValidationEventHandler += new ValidationEventHandler(ValidationCallBack);
        settings.ValidationType = ValidationType.Schema;

        //Create the schema validating reader.
        XmlReader vreader = XmlReader.Create(filename, settings);

        while (vreader.Read()) { }

        //Close the reader.
        vreader.Close();
    }

    //Display any warnings or errors.
    private static void ValidationCallBack(object sender, ValidationEventArgs args)
    {
        if (args.Severity == XmlSeverityType.Warning)
            Console.WriteLine("\tWarning: Matching schema not found.  No validation occurred." + args.Message);
        else
            Console.WriteLine("\tValidation error: " + args.Message);

    }
}

The preceding example uses the following input files.

<?xml version='1.0'?>
<bookstore xmlns="urn:bookstore-schema" xmlns:cd="urn:cd-schema">
  <book genre="novel">
    <title>The Confidence Man</title>
    <price>11.99</price>
  </book>
  <cd:cd>
    <title>Americana</title>
    <cd:artist>Offspring</cd:artist>
    <price>16.95</price>
  </cd:cd>
</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>