HTML and CSS Reference
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application. So, there is no one-to-one mapping between the ASP.NET application and the offline
application. One ASP.NET application may include multiple independent offline applications. Each such
offline application needs its own cache manifest. There is no rigid requirement for the cache manifest's file
extension, but .appcache and .manifest are commonly used.
Simply creating a cache manifest file isn't sufficient. All the web pages belonging to that offline
application should refer the cache manifest. This way, whenever a browser downloads a web page, it
knows that this page is part of an offline application. Additionally, the cache manifest tells the browser
what resources the page requires (images, script files, and so on) so that the browser can ensure
availability of those resources.
As mentioned, a cache manifest file can have any developer-defined extension. You need to inform IIS
about the file extension you're using for your cache manifest file and associated MIME type. Without this
information, IIS may not send the cache manifest to the browser, and the browser can't cache the required
Although offline applications behave like stand-alone applications, at some point in their lifetime they
may need to interact with the web server. Suppose, for example, that you've developed a JavaScript-
intensive game as an offline application. This means the end user doesn't need network connectivity while
playing the game. However, at the end, the game may need to go online to store the user's score in an
online account or profile. In this case, you need to check whether a network connection is available and, if
so, perform the required data transfer. This step is, of course, optional and depends primarily on the
nature of the application.
The following sections examine in detail the steps you follow to build an offline application. You
develop a simple Web Forms-based offline application that uses the topics you've learn about. This offline
application displays a JavaScript-driven digital clock on a web page (see Figure 8-2). There is also a
provision to send the time shown on the clock to the server for further processing.
Figure 8-2. Clock offline application
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