Substitution Web Server Control Declarative Syntax
Specifies a section on an output-cached Web page that is exempt from caching. At this location, dynamic content is retrieved and substituted for the Substitution control.
<asp:Substitution
EnableTheming="True|False"
EnableViewState="True|False"
ID="string"
MethodName="string"
OnDataBinding="DataBinding event handler"
OnDisposed="Disposed event handler"
OnInit="Init event handler"
OnLoad="Load event handler"
OnPreRender="PreRender event handler"
OnUnload="Unload event handler"
runat="server"
SkinID="string"
Visible="True|False"
/>
Remarks
Use the Substitution control to specify a section on an output-cached Web page where you want dynamic content substituted for the control. The Substitution control offers a simplified solution to partial page caching for pages where the majority of the content is cached. You can output-cache the entire page, and then use Substitution controls to specify the parts of the page that are exempt from caching.
For more information on the Substitution control, see Substitution Web Server Control Overview.
Example
The following code example demonstrates how to add a Substitution control declaratively to an output-cached Web page. When the page loads, the current date and time are displayed to the user in a label. This section of the page is cached and updated every 60 seconds. When the Substitution control executes, it calls the GetCurrentDateTime method. The string returned by the GetCurrentDateTime is displayed to the user. This section of the page is not cached and is updated each time the page is refreshed.
<%@ outputcache duration="60" 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" language="VB">
Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
' Display the current date and time in the label.
' Output caching applies to this section of the page.
CachedDateLabel.Text = DateTime.Now.ToString()
End Sub
' The Substitution control calls this method to retrieve
' the current date and time. This section of the page
' is exempt from output caching.
Shared Function GetCurrentDateTime(ByVal context As HttpContext) As String
Return DateTime.Now.ToString()
End Function
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
<title>Substitution Class Example</title>
</head>
<body>
<form id="Form1" runat="server">
<h3>Substitution Class Example</h3>
<p>This section of the page is not cached:</p>
<asp:substitution id="Substitution1"
methodname="GetCurrentDateTime"
runat="Server">
</asp:substitution>
<br />
<p>This section of the page is cached:</p>
<asp:label id="CachedDateLabel"
runat="Server">
</asp:label>
<br /><br />
<asp:button id="RefreshButton"
text="Refresh Page"
runat="Server">
</asp:button>
</form>
</body>
</html>
<%@ outputcache duration="60" 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" language="C#">
void Page_Load(object sender, System.EventArgs e)
{
// Display the current date and time in the label.
// Output caching applies to this section of the page.
CachedDateLabel.Text = DateTime.Now.ToString();
}
// The Substitution control calls this method to retrieve
// the current date and time. This section of the page
// is exempt from output caching.
public static string GetCurrentDateTime (HttpContext context)
{
return DateTime.Now.ToString ();
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Substitution Class Example</title>
</head>
<body>
<form id="form1" runat="server">
<h3>Substitution Class Example</h3>
<p>This section of the page is not cached:</p>
<asp:substitution id="Substitution1"
methodname="GetCurrentDateTime"
runat="Server">
</asp:substitution>
<br />
<p>This section of the page is cached:</p>
<asp:label id="CachedDateLabel"
runat="Server">
</asp:label>
<br /><br />
<asp:button id="RefreshButton"
text="Refresh Page"
runat="Server">
</asp:button>
</form>
</body>
</html>