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You can also react to the ObjectDisposing event to perform cleanup. The ObjectDisposing event is fired just before the data access object is released (before the page is served). Usually, you won t need to use the ObjectDisposing event because a better alternative exists place your cleanup code in a dedicated Dispose() method inside your data access class. As long as you implement IDisposable, the ObjectDataSource will automatically call your Dispose() method. (To get a painless implementation of IDisposable for free, just derive your data access class from the System.ComponentModel.Component class and override the Dispose() method.)

string firstName = gridEmployees.SelectedRow.Cells[2].Text; string lastName = gridEmployees.SelectedRow.Cells[3].Text; lblRegionCaption.Text = "Regions that " + firstName + " " + lastName + " (employee " + ID.ToString() + ") is responsible for:"; } Figure 10-7 shows the result.

At this point you re probably wondering where ASP.NET stores session information and how it serializes and deserializes it. In classic ASP the session state is implemented as a free-threaded COM , object that s contained in the asp.dll library. In ASP.NET, the programming interface is nearly identical, but the underlying implementation is quite a bit different. As you saw in 5, when ASP.NET handles an HTTP request, it flows through a pipeline of different modules that can react to application events. One of the modules in this chain is the SessionStateModule (in the System.Web.SessionState namespace). The SessionStateModule generates the session ID, retrieves the session data from external state providers, and binds the data to the call context of the request. It also saves the session state information when the page is finished processing. However, it s important to realize that the SessionStateModule doesn t actually store the session data. Instead, the session state is persisted in external components, which are named state providers. Figure 6-5 shows this interaction. Session state is another example of ASP.NET s pluggable architecture. A state provider is any class that implements the IStateClientManager interface, which means you can customize how session state works simply by building (or purchasing) a new .NET component. ASP.NET includes three prebuilt state providers, which allow you to store information in process, in a separate service, or in a SQL Server database.

Earlier, you saw how you could use the SqlDataSource to execute parameterized commands. The same feat is possible with the ObjectDataSource, if you provide a suitable select method that accepts one or more parameters. You can then map each parameter to a control value, query string argument, and so on. To try this, you can use the EmployeeDB.GetEmployee() method, which retrieves a single employee by ID number. Here s the method declaration:

You don t need to create a new column to support row selection. Instead, you can turn an existing column into a link. This technique is commonly used to allow users to select rows in a table by the unique ID value. To use this technique, remove the CommandField column and add a ButtonField column instead. Then, set the DataTextField to the name of the field you want to use. <asp:ButtonField ButtonType="Button" DataTextField="EmployeeID" /> This field will be underlined and turned into a link that, when clicked, will post back the page and trigger the GridView.RowCommand event. You could handle this event, determine which row has been clicked, and programmatically set the SelectedIndex property. However, you can use an easier method. Instead, just configure the link to raise the SelectedIndexChanged event by specifying a CommandName with the text Select, as shown here: <asp:ButtonField CommandName="Select" ButtonType="Button" DataTextField="EmployeeID" /> Now clicking the data field automatically selects the record.

The final ingredient in the puzzle is how the cookie is tracked from one request to the next. For session state to work, the client needs to present the appropriate session ID with each request. You can accomplish this in two ways: Using cookies: In this case, the session ID is transmitted in a special cookie (named ASP.NET_SessionId), which ASP.NET creates automatically when the session collection is used. This is the default, and it s also the same approach that was used in earlier versions of ASP. Using modified URLs: In this case, the session ID is transmitted in a specially modified (or munged ) URL. This is a new feature in ASP.NET that allows you to create applications that use session state with clients that don t support cookies. You ll learn more about how to configure cookieless sessions and different session state providers later in the Configuring Session State section.