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

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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

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ASP.NET Server Controls

• HTML Server Controls– HTML server controls are HTML tags understood by the

server

• Web Server Controls– Web server controls are special ASP.NET tags understood

by the server.

– According to the browser type and version, Web server controls can be mapped to HTML elements in different ways

• We should use Web Server Controls

• Standard on ToolBox

Windows Programs

• Web applications are different from Windows programs

• Developers’ Code– Sub Main– EXE file– Class variables to maintain state information– Example: employee displayed on

IndividualForm of Prog6 of CS33404

Web Applications

• IIS running as interface

• ASP.NET running to generate dynamic pages

• Developers’ code– No Sub Main– Classes are in DLL files– Objects are created and removed by ASP.NET

(too many objects to store in memory)– Class variables cannot keep state information

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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

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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.

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What is a Session?

• Running a Windows program– The time period between starting a program and

terminating the program

• Session of Web Sites– Session start: the first visit to any page of the site– Session end: no way to know if the user is still

there or not– Session Time Out

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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

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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

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Global.asax

• Application_Start

• Application_End

• Application_Error

• Session_Start

• Session_End

Prog2All Session Variables Begin with Prog2_

• 6 Session variables• String

– Prog2_ID– Prog2_Price– Prog2_Quantity– Prog2_SubTotal– Prog2_Tax– Prog2_GrandTotal

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• 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(. . .)

End Sub

Sub Application_Error(. . .)

End Sub

Sub Session_Start(. . .)

Session("Prog2_ProductID") = ""

Session("Prog2_ProductIPrice") = ""

Session("Prog2_ProductQuantity") = ""

Session("Prog2_Computed") = False

End Sub

Sub Session_End(. . .)

End Sub

</script> 13

Session Variables

• Don’t need to be declared

• We need to remember the type of session variables

• Initialized at the session start– Inside file Global.asax

• Accessed and updated inside event procedures

• Restored in Page Load event procedure

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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.

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Update and Restore Session Variables

Protected Sub Button1_Click(…) Handles Button1.Click

‘ Computing result

. . .

‘ Store state information

Session("Lab2_ProductID") = txtID.Text

Session("Lab2_ProductIPrice") = txtPrice.Text

End Sub

Protected Sub Page_Load(…) Handles Me.Load

txtID.Text = Session("Lab2_ProductID")

txtPrice.Text = Session("Lab2_ProductIPrice")

End Sub16

User Input Will Be Lost!

‘ For each request, the event procedure will be invoked

‘ and we never get the user input.




End Sub

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Visiting Dynamic Pages

• First Visit

(can use the initial value of session variables)

• Return Visit from other pages

(need to restore the value of session variables)

• Post Back

(keep user input)

• (Call Back)

• (Cross Post Back)18

Post Back

• User Interaction– Clicking on a button– . . .

• User Input

• Event Procedures

• New version of the same page generated

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Page.IsPostBack Property

Click Here

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Generating Dynamic Pages

• First Visit– No user input

• Return Visit from other pages– No user input– May need to restore Session Data (Prog2)

• Post Back– Event procedures with user input– May access and/or update Session Data

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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

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Page Load Event Procedure


‘ first or return visits

‘ restore Session data

‘ Else is not needed!Else is not needed!

End If

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Update and Restore Session Variables

Protected Sub Button1_Click(…) Handles Button1.Click

‘ Computing result

. . .

Session("Lab2_ProductID") = txtID.Text

Session("Lab2_ProductIPrice") = txtPrice.Text

End Sub





End If

End Sub24

Button Reset

•The reset button make it easier

•CauseValidation: False!

•Reset session variables

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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" />

<system.web>

<configuration>

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Web.config


<configuration>

<system.web>

<compilation debug=“true" targetFramework="4.5" />

<system.web>

<configuration>

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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" />

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Web.config


<configuration>

<system.web>


<system.web>

<configuration>

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Web.config<?xml version="1.0"?>

<configuration>

<system.web>

<compilation debug="true" targetFramework="4.5"

urlLinePragmas="true“ />

<customErrors mode="Off"/>


<system.web>

<configuration>

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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

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Page Directives<%@ Page Language="VB" AutoEventWireup="false"

CodeFile="OrderingProduct.aspx.vb"

Inherits="Prog2_OrderingProduct" %>

AutoEventWireupTrue: 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 events33

Style

Display

z-index

Width: 15%

Padding-left: 10%

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<br /> <br />

<asp:TextBox ID="txtID" runat="server" style=“position: relative; margin-left: 17.5%; width: 15%; display: inline-block" BorderStyle="Solid" AutoPostBack="false" TabIndex="0"></asp:TextBox> <asp:TextBox ID="txtPrice" runat="server" style="position: relative; margin-left:10%; width: 15%; display: inline-block; text-align:right" BorderStyle="Solid" AutoPostBack="false" tabindex="1"></asp:TextBox>

<br /> <br />

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Prog2

You lose five points for each late day!

Even the server is having issues!

Documents

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