Navigating XML information items using ASP.NET 2.0 and VB.NET

This tutorial will show you how to navigate XML information items in ASP.NET 2.0 using VB.NET.

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First, import the namespace of System.XML and System.XML.XPath

The System.Xml.XPath namespace contains the classes that define a cursor model for navigating and editing XML information items as instances of the XPath 2.0 Data Model. In this sample, we will use the classes of XPathDocument, XPathNavigator, XPathExpression and XPathNodeIterator under this namespace .

Imports System.Xml
Imports System.Xml.XPath
Imports System.Data

The Button1_Click event is to perform the navgating XML infomration items fuction. The results will be displayed in the textbox. There are 4 classes we applied.

XPathDocument: Provides a fast, read-only, in-memory representation of an XML document using the XPath data model.

XPathNavigator: Provides a cursor model for navigating XML data.

XPathExpression: Provides a typed class that represents a compiled XPath expression.

XPathNodeIterator: Provides an iterator over a selected set of nodes.

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim doc = New XPathDocument(Server.MapPath("Demo.xml"))
Dim nav = doc.CreateNavigator()

Dim xpathExpress = nav.Compile("//bk:Book[position()" + Me.ddownlist.SelectedValue.Trim() + Me.txtNum.Text.Trim() + "]")
'use AddNamespace
Dim xmlManager = New XmlNamespaceManager(nav.NameTable)
xmlManager.AddNamespace("bk", "http://myserver/myschemas/Books")
xpathExpress.SetContext(xmlManager)

Dim xIterator = nav.Select(xpathExpress)
Me.TextBox1.Text = ""
Me.TextBox1.ForeColor = System.Drawing.Color.Empty
Do While xIterator.MoveNext()

Me.TextBox1.Text = Me.TextBox1.Text + ControlChars.CrLf + xIterator.Current.Value

Loop
If (xIterator.Count.Equals(0)) Then

Me.TextBox1.Text = "There is no xml data in the condition."
Me.TextBox1.ForeColor = System.Drawing.Color.Red

End If

End Sub

The contents of Demo.xml:

<?xml version='1.0' encoding='utf-8'?>
<bk:Books xmlns:bk='http://myserver/myschemas/Books'>

<bk:Book>

<bk:Title>Just XML</bk:Title>

</bk:Book> <bk:Book>

<bk:Title>Professional XML</bk:Title>

</bk:Book> <bk:Book>

<bk:Title>XML Step by Step</bk:Title>

</bk:Book> <bk:Book>

<bk:Title>XML By Example</bk:Title>

</bk:Book>

</bk:Books>

The front end Default.aspx page looks something like this:

<body>

<fieldset><legend>Select xml data with XPath</legend>

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" CellPadding="4"
Font-Size="Smaller" ForeColor="#333333" GridLines="None" RowHeaderColumn="Title"
Width="205px">

</asp:GridView> <br />

<asp:Label ID="Label1" runat="server" Text="Select Item Position:"></asp:Label> <asp:DropDownList
ID="ddownlist" runat="server">

<asp:ListItem><</asp:ListItem>
<asp:ListItem><=</asp:ListItem>
<asp:ListItem>></asp:ListItem>
<asp:ListItem>>=</asp:ListItem>

</asp:DropDownList>

<asp:TextBox ID="txtNum" runat="server" Width="57px">2</asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="txtNum"
ErrorMessage="Please input integer number."></asp:RequiredFieldValidator><br />
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Search" /><br />
<asp:TextBox ID="TextBox1" runat="server" Height="88px" TextMode="MultiLine" Width="237px"></asp:TextBox>

</fieldset>

</div>
</form>

</body>

The flow for the code behind page as follows.

Imports System.Xml
Imports System.Xml.XPath
Imports System.Data
Partial Class _Default

Inherits System.Web.UI.Page
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

Me.TextBox1.Text = Me.TextBox1.Text + ControlChars.CrLf + xIterator.Current.Value

Loop
If (xIterator.Count.Equals(0)) Then

Me.TextBox1.Text = "There is no xml data in the condition."
Me.TextBox1.ForeColor = System.Drawing.Color.Red

End If

End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

If Not Page.IsPostBack Then

Dim myDs = New DataSet()
myDs.ReadXml(Server.MapPath("Demo.xml"))
Me.GridView1.DataSource = myDs
Me.GridView1.DataBind()

End If

End Sub

End Class

Download the Full Working Version of this Project written with Visual Studio.NET VB.NET 2005 Here!

Looking for the C#.NET 2005 Version? Click Here!

Looking for more ASP.NET Tutorials? Click Here!