ASP.NET 4 Unleased - p 139 pptx

SetETagFromFileDependencies—Enables you to set the ETag HTTP header from the time stamps of all files on which the page is dependent... SetLastModifiedFromFileDependencies—Enables you to

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<%= DateTime.Now.ToString(“T”) %>

<hr />

<asp:GridView

id=”grdMovies”

DataSourceID=”srcMovies”

Runat=”server” />

<asp:SqlDataSource

id=”srcMovies”

ConnectionString=”<%$ ConnectionStrings:Movies %>”

SelectCommand=”SELECT Title, Director FROM Movies”

<a href=”AddMovie.aspx”>Add Movie</a>

</div>

</form>

</body>

</html>

The page in Listing 29.12 contains a DetailsView control that enables you to add a new

movie When you insert a new movie into the database, the

Response.RemoveOutputCacheItem() method is called to remove the MovieList.aspx page

from the cache Because this method accepts only a “virtual absolute” path, the

Page.ResolveUrl() method converts the tilde into the application root path

LISTING 29.12 AddMovie.aspx

<%@ Page Language=”C#” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”

“http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>

protected void dtlMovie_ItemInserted(object sender,

➥DetailsViewInsertedEventArgs e)

{

HttpResponse.RemoveOutputCacheItem(Page.ResolveUrl(“~/MovieList.aspx”));

Response.Redirect(“~/MovieList.aspx”);

}

</script>

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</head>

<body>

<div>

<h1>Add Movie</h1>

<asp:DetailsView

id=”dtlMovie”

DefaultMode=”Insert”

AutoGenerateRows=”false”

AutoGenerateInsertButton=”true”

Runat=”server” OnItemInserted=”dtlMovie_ItemInserted”>

<asp:BoundField

DataField=”Title”

HeaderText=”Title:” />

<asp:BoundField

DataField=”Director”

HeaderText=”Director:” />

</Fields>

</asp:DetailsView>

<asp:SqlDataSource

id=”srcMovies”

InsertCommand=”INSERT Movies (Title, Director)

VALUES (@Title, @Director)”

</div>

</form>

</body>

</html>

The Response.RemoveOutputCacheItem() method enables you to remove only one page

from the cache at a time If you need to remove multiple pages, you can create a key

dependency, which enables you to create a dependency between one item in the cache and

another item When the second item is removed from the cache, the first item is removed

automatically

For example, the page in Listing 29.13 also displays a list of movies However, the page is

cached with a dependency on an item in the cache named Movies

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LISTING 29.13 MovieListKeyDependency.aspx

<%@ OutputCache Duration=”3600” VaryByParam=”none” %>

protected void Page_Load(object sender, EventArgs e)

{

Cache.Insert(“Movies”, DateTime.Now);

Response.AddCacheItemDependency(“Movies”);

}

</script>

<title>Movie List Key Dependency</title>

</head>

<body>

<div>

<hr />

<asp:GridView

id=”grdMovies”

<asp:SqlDataSource

id=”srcMovies”

SelectCommand=”SELECT Title, Director FROM Movies”

<a href=”AddMovieKeyDependency.aspx”>Add Movie</a>

</div>

</form>

</body>

</html>

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The page in Listing 29.14 enables you to add a new movie to the Movies database table

When the new movie is inserted, the Movies item is removed, and any pages dependent

on the Movies item are dropped from the cache automatically

LISTING 29.14 AddMovieKeyDependency.aspx

protected void dtlMovie_ItemInserted(object sender,

➥DetailsViewInsertedEventArgs e)

{

Cache.Remove(“Movies”);

Response.Redirect(“~/MovieListKeyDependency.aspx”);

}

</script>

<title>Add Movie Key Dependency</title>

</head>

<body>

<div>

<h1>Add Movie</h1>

<asp:DetailsView

id=”dtlMovie”

DefaultMode=”Insert”

AutoGenerateRows=”false”

AutoGenerateInsertButton=”true”

Runat=”server” OnItemInserted=”dtlMovie_ItemInserted”>

<asp:BoundField

DataField=”Title”

HeaderText=”Title:” />

<asp:BoundField

DataField=”Director”

HeaderText=”Director:” />

</Fields>

</asp:DetailsView>

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<asp:SqlDataSource

id=”srcMovies”

InsertCommand=”INSERT Movies (Title, Director)

VALUES (@Title, @Director)”

</div>

</form>

</body>

</html>

Manipulating the Page Output Cache Programmatically

If you need more control over how ASP.NET Framework caches pages, then you can

work directly with the HttpCachePolicy class This class is exposed by the

Response.Cache property

The HttpCachePolicy class includes properties and methods that enable you to perform

programmatically all the tasks that you can perform with the <%@ OutputCache %>

direc-tive You also can use the methods of this class to manipulate the HTTP cache headers

that are sent to proxy servers and browsers

This class supports the following properties:

VaryByHeaders—Gets the list of headers that are used to vary cache output

VaryByParams—Gets the list of query string and form parameters used to vary cache

output

The HttpCachePolicy class also supports the following methods:

AddValidationCallback—Enables you to create a method called automatically before

a page is retrieved from the cache

AppendCacheExtension—Enables you to add custom text to the Cache-Control HTTP

header

SetAllowResponseInBrowserHistory—Enables you to prevent a page from appearing

in the browser history cache

SetCacheability—Enables you to set the Cache-Control header and the server

cache

SetETag—Enables you to set the ETag HTTP header

SetETagFromFileDependencies—Enables you to set the ETag HTTP header from the

time stamps of all files on which the page is dependent

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SetLastModified—Enables you to set the Last-Modified HTTP header

SetLastModifiedFromFileDependencies—Enables you to set the Last-Modified

HTTP header from the time stamps of all files on which the page is dependent

SetMaxAge—Enables you to set the Cache-Control:max-age HTTP header

SetNoServerCaching—Enables you to disable web server caching

SetNoStore—Enables you to send a Cache-Control:no-store HTTP header

SetNoTransform—Enables you to send a Cache-Control:no-transform HTTP header

SetOmitVaryStar—Enables you to not send the vary:* HTTP header

SetProxyMaxAge—Enables you to set the Cache-Control:s-maxage HTTP header

SetRevalidation—Enables you to set the Cache-Control HTTP header to either

must-revalidation or proxy-revalidate

SetSlidingExpiration—Enables you to set a sliding expiration policy

SetValidUntilExpires—Enables you to prevent a page from expiring from the web

server cache when a browser sends a Cache-Control header

SetVaryByCustom—Enables you to set the string passed to the

GetVaryByCustomString() method in the Global.asax file

For example, the page in Listing 29.15 programmatically places a page in the output

cache The page is cached on the browser, proxy servers, and web server for 15 seconds

LISTING 29.15 ProgramOutputCache.aspx

void Page_Load()

{

Response.Cache.SetCacheability(HttpCacheability.Public);

Response.Cache.SetExpires(DateTime.Now.AddSeconds(15));

Response.Cache.SetMaxAge(TimeSpan.FromSeconds(15));

Response.Cache.SetValidUntilExpires(true);

Response.Cache.SetLastModified(DateTime.Now);

Response.Cache.SetOmitVaryStar(true);

}

</script>

<title>Program OutputCache</title>

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</head>

<body>

<div>

<a href=”ProgramOutputCache.aspx”>Request this Page</a>

</div>

</form>

</body>

</html>

Clearly, it is more difficult to enable Page Output Caching programmatically than

declara-tively You need to call many methods to cache a page in the same way as you can with a

single <%@ OutputCache %> directive However, programmatically manipulating the cache

provides you with fine-grained control over the HTTP headers sent to proxy servers and

browsers

Creating Page Output Cache Profiles

Instead of configuring Page Output Caching for each page in an application, you can

configure Page Output Caching in a web configuration file and apply the settings to

multiple pages You can create a Cache Profile Creating Cache Profiles makes your website

easier to manage

For example, the web configuration file in Listing 29.16 contains the definition for a

Cache Profile named Cache1Hour that caches a page for one hour

LISTING 29.16 Web.Config

<?xml version=”1.0”?>

<system.web>

</outputCacheProfiles>

</outputCacheSettings>

</caching>

</system.web>

</configuration>

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The page in Listing 29.17 uses the Cache1Hour profile This profile is set with the <%@

OutputCache %> directive’s CacheProfile attribute

LISTING 29.17 OutputCacheProfile.aspx

<%@ OutputCache CacheProfile=”Cache1Hour” %>

<title>Output Cache Profile</title>

</head>

<body>

<div>

</div>

</form>

</body>

</html>

You can set the same caching properties in a Cache Profile as you can set in an individual

page’s <%@ OutputCache %> directive For example, you can set varyByParam,

varyByControl, varyByHeader, and even varyByCustom attributes in a Cache Profile

NOTE

ASP.NET 4 introduces a new feature called Extensible Output Caching, which enables

you to configure a custom output-cache provider that utilizes whatever storage medium

you choose—local disks, cloud-based storage, and so on To learn more about

develop-ing a custom output-cache provider, check out the MSDN website (http://msdn

microsoft.com)

Using Partial Page Caching

In the previous section of this chapter, you learned how to cache the entire output of a

page In this section, you learn how to take advantage of Partial Page Caching to cache

particular regions of a page

Partial Page Caching makes sense when a page contains both dynamic and static content

For example, you might want to cache a set of database records displayed in a page but

not cache a random list of news items displayed in the same page

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In this section, you learn about two methods for enabling Partial Page Caching You can

use post-cache substitution to cache an entire page except for a particular region You can

use User Controls to cache particular regions in a page, but not the entire page

Using Post-Cache Substitution

In some cases, you might want to cache an entire page except for one small area For

example, you might want to display the current username dynamically at the top of a

page but cache the remainder of a page In these cases, you can take advantage of a feature

of ASP.NET Framework called post-cache substitution.

Post-cache substitution is used internally by the AdRotator control Even when you use

Page Output Caching to cache a page that contains an AdRotator control, the content

rendered by the AdRotator control is not cached

You can use post-cache substitution either declaratively or programmatically If you want

to use post-cache substitution declaratively, you can use the ASP.NET Substitution

control For example, the page in Listing 29.18 uses the Substitution control to display

the current time on a page that has been output cached (see Figure 29.6)

FIGURE 29.6 Using the Substitution control.

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LISTING 29.18 SubstitutionControl.aspx

<%@ OutputCache Duration=”15” VaryByParam=”none” %>

public static string GetTime(HttpContext context)

{

return DateTime.Now.ToString(“T”);

}

</script>

<title>Substitution Control</title>

</head>

<body>

<div>

The cached time is: <%= DateTime.Now.ToString(“T”) %>

<hr />

The substitution time is:

<asp:Substitution

id=”Substitution1”

MethodName=”GetTime”

</div>

</form>

</body>

</html>

In Listing 29.18, the time is displayed twice The time displayed in the body of the page is

output cached The time displayed by the Substitution control is not cached

The Substitution control has one important property: MethodName The MethodName

prop-erty 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

Alternatively, you can use post-cache substitution programmatically by using the

Response.WriteSubstitution() method This method is illustrated in the page in

Listing 29.19

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