ASP.NET Tutorial/Cache/Post Cache
NewsRotator control uses the WriteSubstitution() when displaying a random news item.
If you use this control in a page that has been output cached, the NewsRotator control continues to display news items randomly.
using System;
using System.Data;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Collections.Generic;
namespace myControls
{
public class NewsRotator : WebControl
{
public static string GetNews(HttpContext context)
{
List<String> news = new List<string>();
news.Add("Martians attack!");
news.Add("Moon collides with earth!");
news.Add("Life on Jupiter!");
Random rnd = new Random();
return news[rnd.Next(news.Count)];
}
protected override void RenderContents(HtmlTextWriter writer)
{
Context.Response.WriteSubstitution(GetNews);
}
}
}
Use post-cache substitution programmatically by using the Response.WriteSubstitution() method.
<%@ Page Language="C#" %>
<%@ OutputCache Duration="15" VaryByParam="none" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
public static string GetTime(HttpContext context)
{
return DateTime.Now.ToString("T");
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
<title>Show WriteSubstitution</title>
</head>
<body>
<form id="form1" runat="server">
<div>
The cached time is: <%= DateTime.Now.ToString("T") %>
<hr />
The substitution time is:
<% Response.WriteSubstitution(GetTime); %>
</div>
</form>
</body>
</html>
Using Post-Cache Substitution
The MethodName property accepts the name of a method defined in the page.
The method must be a shared (static) method because an instance of the class is not created when the page is output cached.
<%@ Page Language="C#" %>
<%@ OutputCache Duration="15" VaryByParam="none" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
public static string GetTime(HttpContext context)
{
return DateTime.Now.ToString("T");
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
<title>Substitution Control</title>
</head>
<body>
<form id="form1" runat="server">
<div>
The cached time is: <%= DateTime.Now.ToString("T") %>
<hr />
The substitution time is:
<asp:Substitution
id="Substitution1"
MethodName="GetTime"
Runat="server" />
</div>
</form>
</body>
</html>