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How to: Transform XML by Using LINQ (Visual Basic)

  • Artikkeli

XML Literals make it easy to read XML from one source and transform it to a new XML format. You can take advantage of LINQ queries to retrieve the content to transform, or change content in an existing document to a new XML format.

The example in this topic transforms content from an XML source document to HTML to be viewed in a browser.

Note

Your computer might show different names or locations for some of the Visual Studio user interface elements in the following instructions. The Visual Studio edition that you have and the settings that you use determine these elements. For more information, see Personalizing the IDE.

To transform an XML document

  1. In Visual Studio, create a new Visual Basic project in the Console Application project template.

  2. Double-click the Module1.vb file created in the project to modify the Visual Basic code. Add the following code to the Sub Main of the Module1 module. This code creates the source XML document as an XDocument object.

    Dim catalog =
  <?xml version="1.0"?>
    <Catalog>
      <Book id="bk101">
        <Author>Garghentini, Davide</Author>
        <Title>XML Developer's Guide</Title>
        <Price>44.95</Price>
        <Description>
          An in-depth look at creating applications
          with <technology>XML</technology>. For
          <audience>beginners</audience> or
          <audience>advanced</audience> developers.
        </Description>
      </Book>
      <Book id="bk331">
        <Author>Spencer, Phil</Author>
        <Title>Developing Applications with Visual Basic .NET</Title>
        <Price>45.95</Price>
        <Description>
          Get the expert insights, practical code samples,
          and best practices you need
          to advance your expertise with <technology>Visual
          Basic .NET</technology>.
          Learn how to create faster, more reliable applications
          based on professional,
          pragmatic guidance by today's top <audience>developers</audience>.
        </Description>
      </Book>
    </Catalog>

    How to: Load XML from a File, String, or Stream.

  3. After the code to create the source XML document, add the following code to retrieve all the <Book> elements from the object and transform them into an HTML document. The list of <Book> elements is created by using a LINQ query that returns a collection of XElement objects that contain the transformed HTML. You can use embedded expressions to put the values from the source document in the new XML format.

    The resulting HTML document is written to a file by using the Save method.

    Dim htmlOutput =
  <html>
    <body>
      <%= From book In catalog.<Catalog>.<Book>
          Select <div>
                   <h1><%= book.<Title>.Value %></h1>
                   <h3><%= "By " & book.<Author>.Value %></h3>
                    <h3><%= "Price = " & book.<Price>.Value %></h3>
                    <h2>Description</h2>
                    <%= TransformDescription(book.<Description>(0)) %>
                    <hr/>
                  </div> %>
    </body>
  </html>

htmlOutput.Save("BookDescription.html")

  4. After Sub Main of Module1, add a new method (Sub) to transform a <Description> node into the specified HTML format. This method is called by the code in the previous step and is used to preserve the format of the <Description> elements.

    This method replaces sub-elements of the <Description> element with HTML. The ReplaceWith method is used to preserve the location of the sub-elements. The transformed content of the <Description> element is included in an HTML paragraph (<p>) element. The Nodes property is used to retrieve the transformed content of the <Description> element. This ensures that sub-elements are included in the transformed content.

    Add the following code after Sub Main of Module1.

    Public Function TransformDescription(ByVal desc As XElement) As XElement

  ' Replace <technology> elements with <b>.
  Dim content = (From element In desc...<technology>).ToList()

  If content.Count > 0 Then
    For i = 0 To content.Count - 1
      content(i).ReplaceWith(<b><%= content(i).Value %></b>)
    Next
  End If

  ' Replace <audience> elements with <i>.
  content = (From element In desc...<audience>).ToList()

  If content.Count > 0 Then
    For i = 0 To content.Count - 1
      content(i).ReplaceWith(<i><%= content(i).Value %></i>)
    Next
  End If

  ' Return the updated contents of the <Description> element.
  Return <p><%= desc.Nodes %></p>
End Function

  5. Save your changes.

  6. Press F5 to run the code. The resulting saved document will resemble the following:

    <?xml version="1.0"?>
<html>
  <body>
    <div>
      <h1>XML Developer's Guide</h1>
      <h3>By Garghentini, Davide</h3>
      <h3>Price = 44.95</h3>
      <h2>Description</h2>
      <p>
        An in-depth look at creating applications
        with <b>XML</b>. For
        <i>beginners</i> or
        <i>advanced</i> developers.
      </p>
      <hr />
    </div>
    <div>
      <h1>Developing Applications with Visual Basic .NET</h1>
      <h3>By Spencer, Phil</h3>
      <h3>Price = 45.95</h3>
      <h2>Description</h2>
      <p>
        Get the expert insights, practical code
        samples, and best practices you need
        to advance your expertise with <b>Visual
        Basic .NET</b>. Learn how to create faster,
        more reliable applications based on
        professional, pragmatic guidance by today's
        top <i>developers</i>.
      </p>
      <hr />
    </div>
  </body>
</html>

See also