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eSortExpression = "LastName, FirstName"; } } You could take this sorting approach one step further and cascade searches over any arbitrary collection of columns by storing the user s past sort selections in view state and using them to build a larger sort expression One more technique is available to you You can sort the GridView programmatically by calling the GridViewSort() method and supplying a sort expression This could come in handy if you want to presort a lengthy data report before presenting it to the user It also makes sense if you want to allow the user to choose from a list of predefined sorting options (listed in another control) rather than use column-header clicks Figure 10-9 shows an example When an item is selected from the list, the sort is applied with this code:.

The GridView control has built-in support for pagination. You can use simple pagination with both the SqlDataSource and ObjectDataSource. If you re using the ObjectDataSource, you also have the ability to customize the way the paging works for a more efficient and scalable solution.

As a whole, the data source controls are a remarkable innovation for ASP .NET developers. However, you ll still run into situations where you need to step beyond their bounds or even abandon them completely. In the following sections, you ll see how to use the SqlDataSource and ObjectDataSource to deal with a common design requirement additional options in a master-details list.

protected void lstSorts_SelectedIndexChanged(object sender, EventArgs e) { GridView1.Sort(lstSorts.SelectedValue, SortDirection.Ascending); }

By setting a few properties and handling an event, you can make the GridView control manage the paging for you. The GridView will create the links to jump to the previous or next pages and will display the records for the current page without requiring you to manually extract the records by yourself. Before discussing the advantages and disadvantages of this approach, let s see what you need to get this working. The GridView provides several properties designed specifically to support paging, as shown in Table 10-6. Table 10-6. Paging Members of the DataGrid

Earlier, you saw an example that allowed users to browse a list of cities in different regions using two linked controls a DropDownList and a GridView. Best of all, this example could be created using a SqlDataSource or an ObjectDataSource; either way, it doesn t require any custom code. Figure 9-9 shows this example. As convenient as this example is, it presents a problem that s difficult to fix. Because it s impossible to create a drop-down list that doesn t have a selected item (unless it s empty), the first city in the list is automatically selected. Many web applications use a different behavior and add an extra item at the top of the list with text such as (Choose a City) . Selecting this first item has no effect. Additionally, you might want to add an item that allows you to see every city in a single list. Figure 9-13 shows the result you want.

All the examples of repeated-value binding that you ve seen so far show all the records of the data source on a single web page. However, this isn t always ideal in real-world situations. Connecting to a data source that contains hundreds or even thousands of records would produce an extremely large page that would take a prohibitively long amount of time to render and transmit to the client browser. Most websites that display data in tables or lists support record pagination, which means showing a fixed number of records per page and providing links to navigate to the previous or next pages to display other records. For example, you have no doubt seen this functionality in search engines that can return thousands of matches. The GridView control has built-in support for pagination. You can use simple pagination with both the SqlDataSource and ObjectDataSource. If you re using the ObjectDataSource, you also have the ability to customize the way the paging works for a more efficient and scalable solution.