.net pdf 417

.net pdf 417

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If you have an existing web application created with Visual Studio .NET 2002 or 2003, you can open the project or solution file using the File Open Project command. When you do, Visual Studio begins the Conversion Wizard. The Conversion Wizard is exceedingly simple. It prompts you to choose whether to create a backup and, if so, where it should be placed (see Figure 2-3). If this is your only copy of the application, a backup is a good idea in case some aspects of your application can t be converted successfully. Otherwise, you can skip this option.

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.

All the list controls are essentially the same. The only differences are the way they render themselves in HTML and whether or not they support multiple selection. Figure 9-2 shows a test page that displays all the list controls, along with some text that displays the current selection for the controls.

When you click Finish, Visual Studio performs an in-place conversion. The conversion tool is fairly aggressive, and it attempts to convert every web page to use Visual Studio s new code-behind model. Any errors and warnings are added to a conversion log, which you can display when the conversion is complete. In a typical website, the conversion operation runs without any errors but generates a long list of warnings. These inform you when Visual Studio removes precompiled files, changes pages to use automatic event wire-up, and modifies the accessibility of event handlers (switching them from Private to Protected). All of these changes are minor modifications designed to apply the new coding model, which is described in the section The Coding Model later in this chapter. Figure 2-4 shows a sample log.

Figure 9-2. Repeated-value data binding in list controls The controls are declared as follows: <select runat="server" ID="Select1" size="3" DataTextField="Key" DataValueField="Value" /> <select runat="server" ID="Select2" DataTextField="Key" DataValueField="Value" /> <asp:ListBox runat="server" ID="Listbox1" Size="3" DataTextField="Key" DataValueField="Value" /> <asp:DropDownList runat="server" ID="DropdownList1" DataTextField="Key" DataValueField="Value" /> <asp:RadioButtonList runat="server" ID="OptionList1" DataTextField="Key" DataValueField="Value"/> <asp:CheckBoxList runat="server" ID="CheckList1" DataTextField="Key" DataValueField="Value" /> <br /><br /> <asp:Literal runat="server" ID="Result" EnableViewState="False"/> The last control, the Literal control, displays information about the selected items. Its EnableViewState attribute is set to false so that its content will be cleared after every postback. When the page loads for the first time, the code creates a data source and assigns it to all the list controls. In this example, the data object is a Hashtable collection, which contains a series of strings. The Value of the Hashtable collection item returns the actual item text (which is used for the DataTextField), while the Key of the Hashtable collection item returns the key under which the item is indexed. Here s the code for creating and binding the collection: protected void Page_Load(object sender, System.EventArgs e) { if (!Page.IsPostBack) { // Create the data source. Hashtable ht = new Hashtable(3); ht.Add("Lasagna", "Key1");

You can interact with session state using the SystemWebSessionStateHttpSessionState class, which is provided in an ASPNET web page as the built-in Session object The syntax for adding items to the collection and retrieving them is basically the same as for adding items to the view state of a page For example, you might store a DataSet in session memory like this: Session["ds"] = ds; You can then retrieve it with an appropriate conversion operation: ds = (DataSet)Session["ds"]; 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.