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<%@ Page Language="VB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
<title>Custom Cache Dependency Example</title>
</head>
<body>
<form id="Form1" runat="server"> RSS URL:
<asp:TextBox ID="TextBox1" Runat="server"/>
<asp:Button ID="Button1" onclick="Button1_Click" Runat="server"
Text="Get RSS" />
Cached:<asp:Label ID="Label2" Runat="server"></asp:Label><br />
RSS:<br />
<asp:TextBox ID="TextBox2" Runat="server" TextMode="MultiLine"
Width="800px" Height="300px"></asp:TextBox>
</form>
</body>
</html>
<script runat="server">
Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Dim RSSUrl As String = TextBox1.Text
Label2.Text = "Loaded From Cache"
If Cache(TextBox1.Text) Is Nothing Then
Label2.Text = "Loaded Fresh"
Dim itDepends As New RssCacheDependency(RSSUrl, 600)
Cache.Insert(RSSUrl, itDepends.Document, itDepends)
End If
TextBox2.Text = CType(Cache(TextBox1.Text), _
System.Xml.XmlDocument).OuterXml
End Sub
</script>
File: App_Code\RssCacheDependency.vb
Imports System
Imports System.Web
Imports System.Threading
Imports System.Web.Caching
Imports System.Xml
Public Class RssCacheDependency
Inherits CacheDependency
Shared backgroundThread As Timer
Dim howOften As Integer = 900
Dim RSS As XmlDocument
Dim RSSUrl As String
Public Sub New(ByVal URL As String, ByVal polling As Integer)
howOften = polling
RSSUrl = URL
RSS = RetrieveRSS(RSSUrl)
If backgroundThread Is Nothing Then
backgroundThread = New Timer( _
New TimerCallback(AddressOf CheckDependencyCallback), _
Me, (howOften * 1000), (howOften * 1000))
End If
End Sub
Function RetrieveRSS(ByVal URL As String) As XmlDocument
Dim retVal As New XmlDocument
retVal.Load(URL)
Return retVal
End Function
Public Sub CheckDependencyCallback(ByVal Sender As Object)
Dim CacheDepends As RssCacheDependency = _
CType(Sender, RssCacheDependency)
Dim NewRSS As XmlDocument = RetrieveRSS(RSSUrl)
If Not NewRSS.OuterXml = RSS.OuterXml Then
CacheDepends.NotifyDependencyChanged(CacheDepends, EventArgs.Empty)
End If
End Sub
Protected Overrides Sub DependencyDispose()
backgroundThread = Nothing
MyBase.DependencyDispose()
End Sub
Public ReadOnly Property Document() As XmlDocument
Get
Return RSS
End Get
End Property
End Class
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