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Using the Substitution Control

ASP.NET 2.0 provides a new control called the Substitution control, which enables you to insert

dynamic content into a cached web page. For example, you can display the name of an end user, which

is dynamically generated in a cached web page containing some text or images. The

Substitution con-

trol provides a property called

MethodName, which represents the method called to return the dynamic

content. Listing 1-4 shows an example of the

Substitution control in action.

Listing 1-4: Partial Page Caching Using Substitution Control

<%@ Page Language=”C#” %>

<%@ OutputCache Duration=”6000” VaryByParam=”none” %>

static string GetRandomNumber(HttpContext context)

{

int randomNumber;

randomNumber = new System.Random().Next(1, 10000);

return randomNumber.ToString();

}

</script>

<html>

<head>

<title>Use of Substitution control to implement Partial Caching</title>

</head>

<body>

The random number generated is:

<asp:Substitution ID=”Substitution1” MethodName=”GetRandomNumber”

Runat=”Server” />

<p>

The current time is <%= DateTime.Now.ToString(“t”) %>.

It never changes since the page is cached.

</p>

</form>

</body>

</html>

At the top of the page, the OutputCache directive is used to cache the contents of the page in memory.

The

Duration attribute of the OutputCache directive is set to 6000 milliseconds. The VaryByParam

attribute indicates whether or not ASP.NET should consider the parameters passed to the page when

caching. When

VaryByParam is set to none, no parameters will be considered; all users will receive the

same page no matter what additional parameters are supplied. The

MethodName attribute of the

Substitution control is set to a method named GetRandomNumber, which simply returns a random

number between 1 and 10,000. Note that the return value of the

GetRandomNumber method is a string,

because the

HttpResponseSubstitutionCallback delegate always requires a return type of string.

When you make a request for the page through the browser, you will find that the displayed current

time always remains the same, whereas the portion of the page that is generated by the substitution con-

trol keeps changing every time. In this case, it displays a random number between 1 and 10,000 every

time someone requests the page.

Part I: Introduction

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