Session Variables and Post Back CS 3870/CS 5870 Note04 Session Variables and Post Back

Static Pages and Dynamic Pages Original HTML Universal Reader No User input Smart HTML Input controls User interactive pages

Windows Programs Developers’ Code Sub Main EXE file Class variables to maintain state information Example: values in textboxes on a form

ASP.NET Web Applications IIS running as interface ASP.NET running to generate dynamic pages Developers’ code No Sub Main Page classes are in DLL files Pages are created and removed for each request Page class variables cannot keep state information

Prog2 Visit the ordering page Calculate result Go to page Default Come back to the ordering page Data lost!

Prog2 After a calculation is completed successfully, if the user goes to the start page then comes back to page OrderingProduct.aspx, then all textboxes should show the same data as when the user left the page. All textboxes will be blank if the previous calculation is failed.

Generating Dynamic Pages First Visit No user input Generating pages based on the DLL file Post Back Requesting the same page With user input Return Visit from other pages No information on the visited page

Session Variables To maintain state information for each user on each Web site Maintained by ASP.NET Not by developers’ code Defined inside Global.asax

Session State ASP.NET session state enables you to store and retrieve values for a user as the user navigates ASP.NET pages in a Web application. HTTP is a stateless protocol. This means that a Web server treats each HTTP request for a page as an independent request. The server retains no knowledge of variable values that were used during previous requests. ASP.NET session state identifies requests from the same browser during a limited time window as a session, and provides a way to persist variable values for the duration of that session. By default, ASP.NET session state is enabled for all ASP.NET applications.

What is a Session? Running a Windows program Session of Web Sites The time period between starting a program and terminating the program Session of Web Sites Session start: the first visit of a user to any page of the site Cookies to identify the users Session end: no way to know if the user is still there or not Session Time Out

Session Time Out Length of a session Default value: 30 mins Set in Web.config file Discussed later Session variables are initialized when session starts and updated in event procedures Session variables could be cleared at session end

Visiting Dynamic Pages First Visit Can use the initial value of session variables Post Back Use user input Don’t use session variables to overwrite user input Return Visit from other pages Need to restore the value of session variables

Page.IsPostBack Property Click Here

Session Variables Don’t need to be declared We need to remember the type of session variables Initialized inside Session_Start of Global.asax Accessed and updated inside event procedures Restored in Page Load event procedure

Creating Global.asax Must be inside the Web site main folder, not under any sub-folder Only one global file each Web site Right click Solution or Project Add Add New Global Application Class

Global.asax Application_Start Application_End Application_Error Session_Start Session_End

Prog2 All Session Variables Begin with Prog2_ String Prog2_ID Prog2_Price Prog2_Quantity Prog2_SubTotal Prog2_Tax Prog2_GrandTotal 4 Session variables String Prog2_ID Prog2_Price Prog2_Quantity Boolean Prog2_Computed

Initialize Session Variables <%@ Application Language="VB" %> <script runat="server"> Sub Application_Start(. . .) End Sub Sub Application_End(. . .) Sub Application_Error(. . .) Sub Session_Start(. . .) Session("Prog2_ProductID") = "" Session("Prog2_ProductIPrice") = "" Session("Prog2_ProductQuantity") = "" Session("Prog2_Computed") = False Sub Session_End(. . .) </script>

Update Session Variables Protected Sub Button1_Click(…) Handles Button1.Click ‘ Exit if invalid input ‘ Computing result . . . Session("Lab2_ProductID") = txtID.Text Session("Lab2_ProductIPrice") = txtPrice.Text Session("Prog2_Computed") = True End Sub

Page Load Event Procedure If Not IsPostBack Then ‘ first or return visits ‘ restore Session data Else ‘ Let event procedures ‘ handle the user input End If

Page Load Event Procedure If Not IsPostBack Then ‘ first or return visits ‘ restore Session data ‘ Else is not needed! End If

Restore Session Variables Protected Sub Page_Load(…) Handles Me.Load If Not IsPostBack Then ‘If Session("Prog2_Computed") = True Then txtID.Text = Session("Lab2_ProductID") txtPrice.Text = Session("Lab2_ProductIPrice") ‘End If End If End Sub

User Input Will Be Lost! ‘ For each request, the event procedure will be invoked ‘ and we never get the user input. Protected Sub Page_Load(…) Handles Me.Load txtID.Text = Session("Lab2_ProductID") txtPrice.Text = Session("Lab2_ProductIPrice") End Sub

Button Reset The reset button make it easier CauseValidation: False! Reset session variables

Web Configuration File Creating Web.config file Right click the web site Add new item Web Configuration file Many settings Different levels Machine Site Folder

Web.config <?xml version="1.0"?> <configuration> <system.web> <compilation debug=“true" targetFramework="4.0" />

Web.config <?xml version="1.0"?> <configuration> <system.web> <compilation debug=“true" targetFramework="4.5" />

Session TimeOut Configure file Web.config Short timeout values make development easier <sessionState timeout="1" /> Longer timeout values for production Web sites <sessionState timeout=“30" />

Web.config <?xml version="1.0"?> <configuration> <system.web> <sessionState timeout="1" />

Web.config <?xml version="1.0"?> <configuration> <system.web> <compilation debug="true" targetFramework="4.5" urlLinePragmas="true“ /> <customErrors mode="Off"/> <sessionState timeout="1" />

Compiling Web Pages All code files are precompiled into a single assembly (dll file). Web pages are compiled at the first request Dynamic compilation causes some delay for the first visit

Page Directives AutoEventWireup <%@ Page Language="VB" AutoEventWireup="false" CodeFile="OrderingProduct.aspx.vb" Inherits="Prog2_OrderingProduct" %> AutoEventWireup True: No “handles” for page event procedures (ASP.NET uses procedure name and signature) False: page event procedures must have “handles” Only for page events, not control events