create and print barcode c# <configuration> <system.web> <processModel timeout="60 /> </system.web> </configuration> in VS .NET

Creator Quick Response Code in VS .NET <configuration> <system.web> <processModel timeout="60 /> </system.web> </configuration>

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For more information about application recycling, read the section about the <processModel> tag, in 27.

ASP.NET developers have several options for places they can store values used by applications. In fact, unlike Windows Form applications, ASP or ASP.NET programming is stateless, which means that variables aren t preserved between consecutive requests to the same (or a different) page of the same application. Let me quickly review the advantages and shortcomings of the techniques available to ASP developers for storing state between consecutive requests:

Client-side cookies Because data travels back and forth at each request to a page of the application, you can use this technique only for small amounts of data. Of course, it doesn t work at all if the end user has disabled cookie support in the browser. A great advantage of this technique is that values can be persisted between consecutive visits to the same site. Session variables You can use session variables for larger amounts of data than cookies, but each variable takes memory on the server, so this technique impedes scalability. Worse, ASP sessions don t work on Web gardens or Web farms, so your application can t easily scale out to multiple processes or multiple servers. Finally, sessions are implemented by means of cookies, so they aren t available when cookZ ies are disabled (even though the IIS SDK contains a utility that helps you work around this problem by storing the user ID in the URL instead of a client-side cookie). Application variables You can use this technique only for data shared by all the clients that are connected to the application, so its usefulness is limited, in practice, to caching read-only data such as a database connection string or the table of product codes and prices. Finally, Application values aren t shared among Web gardens and farms. Hidden fields or the query string This approach doesn t require cookie support but can t be implemented easily and usually requires rather contorted coding techniques. Moreover, unlike cookies and session variables, values stored in hidden fields or the query string are lost when the user hits the Back button to return to a page visited previously. Database records plus a cookie or a session variable that holds the key associated with each user This technique is the only one that scales well even with large amounts of data and that (if you use a cookie) can scale out to Web farms. It has some drawbacks, however: it requires extra coding, is slower than all other techniques, and still requires client-side cookie support.

Although all these ASP techniques are still available under ASP.NET, you ll rarely use some of them directly because ASP.NET offers some great alternatives. For example, the Page s ViewState property works exactly like hidden fields, but it s remarkably

Part VI:

simpler to use. As you ll see shortly, ASP.NET supports additional session modes that work across Web farms, can use a database to store user data, and can even function without cookie support. Almost unbelievably, you can switch from regular sessions to these enhanced session modes by simply changing a configuration setting without editZ ing a single line in code. Another important facet of ASP.NET programming is using its caching features corZ rectly. As you ll learn later in this chapter, ASP.NET supports different types of cache techniques. You can cache the output generated by a page and you can cache large data structures in the Cache object. In both cases, you can enforce sophisticated expiZ ration policies. And you can still use other forms of caching as well for example, application and session variables.