asp.net gs1 128

asp.net gs1 128

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Session state is global to your entire application for the current user. Session state can be lost in several ways: If the user closes and restarts the browser. If the user accesses the same page through a different browser window, although the session will still exist if a web page is accessed through the original browser window. Browsers differ on how they handle this situation. If the session times out because of inactivity. By default, a session times out after 20 idle minutes. If the programmer ends the session by calling Session.Abandon(). In the first two cases, the session actually remains in memory, because the web server has no idea that the client has closed the browser or changed windows. The session will linger in memory, remaining inaccessible, until it eventually expires. In addition, session state will be lost when the application domain is re-created. This process happens transparently when you update your web application or change a configuration setting. The application domain may also be recycled periodically to ensure application health, as described in 18. If this behavior is causing a problem, you can store session state information out of process, as described in the next section. With out-of-process state storage, the session information is retained even when the application domain is shut down. Table 6-4 describes the methods and properties of the HttpSessionState class. Table 6-4. HttpSessionState Members

Once you ve associated a sort expression with the column and set the AllowSorting property to true, the GridView will render the headers with clickable links. However, it s up to the data source control to implement the actual sorting logic. How the sorting is implemented depends on the data source you re using. Not all data sources support sorting, but both the SqlDataSource and the ObjectDataSource do.

Don t encrypt view state data if you don t need to do so. The encryption will impose a performance penalty, because the web server needs to perform the encryption and decryption with each postback.

As explained in 8, every DataTable is linked to a default DataView. The DataView is a window onto the DataTable, and it allows you to apply sorting and filtering without altering the structure of the underlying table. You can use a DataView programmatically, but when you use the SqlDataSource it s used implicitly, behind the scenes. However, it s available only when the DataSourceMode property is set to SqlDataSourceMode.DataSet.

In the case of the SqlDataSource, sorting is performed using the built-in sorting capabilities of the DataView class. Essentially, when the user clicks a column link, the DataView.Sort property is set to the sorting expression for that column.

One of the most significant limitations with view state is that it s tightly bound to a specific page. If the user navigates to another page, this information is lost. This problem has several solutions, and the best approach depends on your requirements.

With DataView sorting, the data is retrieved unordered from the database, and the results are sorted in memory. This is not the speediest approach (sorting in memory requires more overhead and is slower than having SQL Server do the same work), but it is more scalable when you add caching to the mix. That s because you can cache a single copy of the data and sort it dynamically in several different ways. ( 11 has much more about this essential technique.) Without DataView sorting, a separate query is needed to retrieve the newly sorted data. Figure 10-8 shows a sortable GridView with column links. Note that no custom code is required for this scenario.

As explained in 8, every DataTable is linked to a default DataView. The DataView is a window onto the DataTable, and it allows you to apply sorting and filtering without altering the structure of the underlying table. You can use a DataView programmatically, but when you use the SqlDataSource it s used implicitly, behind the scenes. However, it s available only when the DataSourceMode property is set to SqlDataSourceMode.DataSet.