Recipe 13.3 Caching Pages Based on Browser Type and Version


13.3.1 Problem

You have a page with static content that you want to cache, but the page is rendered differently for some browsers.

13.3.2 Solution

Add the @ OutputCache directive to the .aspx file of each page you want to cache with the VaryByCustom attribute set to " browser ", as shown here:

 <%@ Page Language="vb" AutoEventWireup="false"           Codebehind="CH13CacheByBrowserVB.aspx.vb"           Inherits="ASPNetCookbook.VBExamples.CH13CacheByBrowserVB" %>  <%@ OutputCache Duration="30" VaryByParam="none"   VaryByCustom="browser" %>  <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html>    ... </html> 

13.3.3 Discussion

The way in which a page is rendered often depends on the characteristics and version number of the browser making the request. ASP.NET handles most of this variation behind the scenes by sensing the browser type and its version and then rendering the HTML and JavaScript in a suitable format.

The variation in a rendered page from one browser type to another can cause problems if you implement caching as described in Recipe 13.1. For example, if a request is made for a page of this type by Internet Explorer 6.x, the page is rendered and stored in the cache. If a request for the same page is made by a Netscape 4.x browser before the cached copy expires , the Internet Explorer 6.x version will be sent to the browser. This generally results in a poorly displayed or improperly functioning page.

ASP.NET provides the ability to cache browser-specific versions of the rendered page by setting the VaryByCustom attribute of the OutputCache element to " browser ". When VaryByCustom is set to " browser ", ASP.NET will check the browser name and major version of the browser making the page request (4.x, 5.x, 6.x, and the like) to see if there is a copy of the rendered page stored in the cache that matches them. If so, the cached version is sent as the response. Otherwise, the page will be rendered as usual, stored in the cache, and then delivered to the browser.

The only VaryByCustom attribute value that ASP.NET provides built-in support for is " browser "; however, with additional coding, this attribute can be used to control the caching of a page by any variation you choose. Recipe 13.4 provides an example of using the VaryByCustom attribute to cache a page based on the browser type and full version number.

The VaryByParam attribute is required even though it is not being used in this example. Setting the value to " none " effectively disables the caching by parameter. Failure to include the VaryByParam attribute will result in a parse error when the page is requested .

13.3.4 See also

Recipe 13.4 for an example of caching based on browser type and full version number

ASP. NET Cookbook
ASP.Net 2.0 Cookbook (Cookbooks (OReilly))
ISBN: 0596100647
EAN: 2147483647
Year: 2006
Pages: 179

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