State in Visual Studio .NET

Creator QR in Visual Studio .NET State

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You saw the If statement back in 4. The Select Case statement is a way to string together multiple If statements in a clearer manner. The Select Case statement opens with the keywords Select Case, followed by the variable being evaluated:

Next is a series of Case statements, each with a different condition that will be compared against the value of myVariable. Each case is followed by some code that runs if the value of the variable matches the condition. Assuming myVariable is a string that represents a size, the Case statements might go like this:

Case "Small" lblMyLabel.Text = "Just a little." Case "Medium" lblMyLabel.Text = "Standard size." Case "Large" lblMyLabel.Text = "Super-size me."

Once a case is matched, only the code for that case is executed; the rest of the code is ignored. In this example, the variable being evaluated is RadioButtonList1. SelectedItem.Value, the value that the user chose.

Run the application and select one of the radio buttons. Then open the drop-down list to see that the items have been populated, as shown in Figure 7-12. Now select one of the other radio buttons. Notice the page posts back immediately, and the content of the drop-down list changes. The first thing that happens in this code is the Text the user selected is added to the session state and associated with the key "cattext" in the dictionary. Similarly, the Value that goes with that text is stored in Session associated with the key "catcode".

Session("cattext") = RadioButtonList1.SelectedItem.Text Session("catcode") = RadioButtonList1.SelectedItem.Value

The Select Case statement is used to populate the drop-down list, depending on the user s selection. In each case, a three-item array called Books is created, but the text for each item varies depending on the Case statement. After Books is populated, it too is saved to Session state:

Then the DisplayStuff( ) helper method is called. Because cattext, catvalue, and books have all been saved in session state, you don t need to pass their values to the helper method. DisplayStuff( ) can retrieve them directly from the Session dictionary, for example, when it concatenates cattext to the string:

str += CType(Session("cattext"), String)

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Remember, you need to use the CType method to convert the value to a string before you can use it. Similarly, the helper method retrieves the books object, uses CType to convert it to an array of strings, and stores it in the new array CatBooks( ):

Dim CatBooks() As String = CType(Session("books"), String( ))

Next, the method uses CatBooks( ) in a loop to populate the drop-down list. Session state is enabled by default and works right out of the box. To increase performance, you can disable session state on a per-page, per-web site, or per-machine basis. To disable session state for a page, include the following highlighted attribute in the Page directive at the top of the markup file:

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" EnableSessionState="False" %>

Valid values for EnableSessionState are True, False, and ReadOnly. ReadOnly provides better performance than True as long as you do not need to edit the values stored in session. How do the values get into session state if it is set to ReadOnly From another page whose value is True.

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To configure session state on a per-web site or per-machine basis, you must edit the configuration file, web.config, in the web site virtual directory. For simple single-server, single-processor web sites with relatively low traffic (measured in hits per minute rather than hundreds or thousands of hits per minute), the default configuration is probably good enough. In more complex or demanding scenarios, you can configure Session state to accommodate a wide range of requirements. This would include the length of the timeout, whether or not browser cookies are used, where the session information is stored (in memory on the local machine, in memory on a state server, or in a database somewhere), and so on.