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Navigating XML information items using ASP.NET and VB
This tutorial will show you how to navigate XML information items in ASP.NET 2.0 using VB.NET.
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 |
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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 |
The contents of Demo.xml:
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<?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> |
The front end Default.aspx page looks something like this:
<body>
<form id="form1" runat="server"> <div>
<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">
<FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" /> <Columns> <asp:BoundField DataField="Title" HeaderText="Title" /> </Columns> <RowStyle BackColor="#EFF3FB" /> <EditRowStyle BackColor="#2461BF" /> <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" /> <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" /> <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" /> <AlternatingRowStyle BackColor="White" /> </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> |
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
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 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 |
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