The System.Xml.XmlUrlResolver Class

Supported Versions

Public Members

Overview

This class is a concrete implementation of the XmlResolver class, and acts as the default resolver class used within the System.Xml library. Its primary function is to resolve references to external DTD, XML Schema, and XSL documents.

Example #1 (VB.NET): How to turn off the XmlResolver on an XmlTextReader object.

In the example below we create an XmlTextReader that reads in the contents of an XML document containing an *invalid* reference to an external Document Type Definition. The XmlTextReader.XmlResolver property is intentionally set to nothing, allowing the XmlTextReader to ignore the DTD reference.

        Dim objXmlTextReader As System.Xml.XmlTextReader

        Dim objXmlUrlResolver As System.Xml.XmlUrlResolver

        Dim strValues As String

        objXmlTextReader = New XmlTextReader("c:\note.xml")

        objXmlTextReader.XmlResolver = Nothing

        strValues = "First Try - no resolver" & CrLf

        While (objXmlTextReader.Read)

            strValues &= objXmlTextReader.ReadInnerXml

        End While

        TextBox1.Text = strValues

Example #2 (VB.NET): How to explicitly assign an XmlUrlResolver object to an XmlTextReader object.

(This is a continuation of our previous example.) We now explicitly create an XmlUrlResolver object and assign it to the XmlTextReader object. By doing so the XmlTextReader.Read method is forced to check the DTD reference. Upon discovering that the reference is invalid, an error is generated and displayed.

            ...

        objXmlUrlResolver = New XmlUrlResolver

        Try

            objXmlTextReader.XmlResolver = objXmlUrlResolver

            strValues &= "Second Try - with resolver" & CrLf

            While (objXmlTextReader.Read)

                strValues &= objXmlTextReader.ReadInnerXml

            End While

        Catch objException As Exception

            strValues &= objException.Message

        End Try

        TextBox1.Text = strValues