XmlDocument.XmlResolver Property


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Sets the XmlResolver to use for resolving external resources.

Namespace:   System.Xml
Assembly:  System.Xml (in System.Xml.dll)

Public Overridable WriteOnly Property XmlResolver As XmlResolver

Property Value

Type: System.Xml.XmlResolver

The XmlResolver to use.

In version 1.1 of the.NET Framework, the caller must be fully trusted in order to specify an XmlResolver.

Exception Condition

This property is set to null and an external DTD or entity is encountered.

The XmlResolver can be used to load DTDs or expand entity references. Using the XmlResolver.Credentials property, you can set credentials on the XmlResolver to access resources stored on a secure network resource.

  • If the document was not loaded using an XmlReader (that is, if it was loaded using a stream, file, and so on) the XmlResolver on the XmlDocument is always used.

  • If the document was loaded with an XmlTextReader, the resolver on the XmlTextReader is used to resolve any DTD references in the DocumentType node. The resolver on the XmlDocument is used to expand any entity references.

  • If the document was loaded with an XmlValidatingReader, the resolver on the XmlDocument is never used.

  • If the document was loaded with a class that extends XmlReader and the XmlReader cannot resolve entities (CanResolveEntity returns false), the XmlResolver on the XmlDocument is used to resolve any references in the DocumentType node and to expand any entity references.


If the XmlDocument is loaded using an XmlReader which had an XmlResolver set to it, the XmlResolver on the XmlReader is not cached by the XmlDocument after Load completes.

In version 1.1 of the.NET Framework, if this property is not set, the trust level of the application determines the default behavior.

Fully trusted code: The document uses a default XmlUrlResolver with no user credentials. If authentication is required to access a network resource, use the XmlResolver property to specify an XmlResolver with the necessary credentials.

Semi-trusted code: The XmlResolver property is set to null. External resources are not resolved.

For more information on security and the XmlResolver property, see Resolving External Resources.

This property is a Microsoft extension to the Document Object Model (DOM).

The following example loads an XML document which includes a reference to a DTD file. The XmlResolver property is used to set the credentials necessary to access the network resource.

Imports System
Imports System.IO
Imports System.Xml
Imports System.Net

public class Sample 

  public shared sub Main()

    ' Supply the credentials necessary access the DTD file stored on the network.
    Dim resolver as XmlUrlResolver = new XmlUrlResolver()
    resolver.Credentials = CredentialCache.DefaultCredentials

    ' Create and load the XmlDocument.
    Dim doc as XmlDocument = new XmlDocument()
    doc.XmlResolver = resolver  ' Set the resolver.

    ' Display the entity replacement text which is pulled from the DTD file.

  end sub
end class

The example uses the following data files as input.


<!DOCTYPE book SYSTEM 'http://myServer/data/books.dtd'>
<book ISBN = '1-861001-57-5'>
  <title>Oberon's Legacy</title>


.NET Framework
Available since 1.1
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