is the caching of pages or portions of pages that are output
to the client. This does not happen automatically. The developer must enable output caching
using either the
OutputCache directive or the
HttpCachePolicy class. Both methods will be described.
Output caching can be applied to an entire page or a portion of the page. To cache only a portion of a page, the caching is applied to a user control contained within the page. This will be described later in this section.
OutputCache directive, like all page directives, goes at the top of the page file. (For a complete description of
page directives, see Chapter 6.) A typical example of an
OutputCache directive looks something like the following:
<%@ OutputCache Duration="60" VaryByParam="*" %>
The full syntax is:
<%@ OutputCache Duration="number of seconds" VaryByParam="parameter list" CacheProfile="" DiskCacheable="" Locaton="Any | Client | Downstream | Server | None" NoStore="" SqlDependency="
table" VaryByControl="control list" VaryByCustom="custom output" VaryByHeader="header list" %>
Only the first two parameters,
VaryByParam, are required, though the
VaryByParam attribute will not be required for user controls if there is a
VaryBy... parameters allow different versions of the cached page to be stored with each version satisfying the combination of conditions being varied.
The various parameters are described in the following ...