Form Handling and State Maintenance

1
Form Handling and State Maintenance

• Major Build-in ASP.NET Objects
• Simple Form Handling
• HTML Forms
• More Complex Form Processing
• State Maintenance Overview
• ViewState and Cookies Variables
• Application and Session Variables
• Navigating Between Web Pages (Forms)

2
Major Build-in ASPX Objects

• Request Object
• Cookies
• Form
• QueryString
• ServerVariables
• ClientCertificate

• Response Object
• Cookies
• (Properties)
• (Methods)

S e r v e r
C l i e n t

• Server Object
• (Properties)
• (Methods)

Application Object Session Object Cache Object
3
Form Data Handling Without PostBack
4
Form Methodpost
greeting.htm

• lthtmlgtltbodygt
• ltform action"greeting.aspx" method"post"gt
• Enter your name
• ltinput type"text" name"guestName"gt ltbrgt
• ltinput type"submit" value"Submit your name"gt
• lt/formgtlt/bodygtlt/htmlgt

greeting.aspx
lthtmlgtltheadgtlttitlegtGreetingslt/titlegtlt/headgt ltbodygt
Hello lt request.form("guestName") gt
! lt/bodygtlt/htmlgt
5
Form Methodget
greeting2.htm
lthtmlgtltbodygt ltform action"greeting2.aspx"
method"get"gt Enter your name ltinput
type"text" name"guestName"gt ltbrgt ltinput
type"submit" value"Submit your
name"gt lt/formgtlt/bodygtlt/htmlgt
greeting2.aspx
lthtmlgtltheadgtlttitlegtGreetingslt/titlegtlt/headgt ltbodygt
Hello lt request.QueryString("guestName") gt
! lt/bodygtlt/htmlgt
6
Query Strings

• A query string is information appended to the end
  of a page's URL. A typical example might look
  like the following
• http//localhost/test.aspx?categorybasicprice10
  0
• In the URL path above, the query string starts
  with the question mark (?) and includes two
  name-value pairs, one called "category" and the
  other called "price."

QueryString
7
Multiple Values of a Variable
http//localhost/aspsimple/list.aspx?foodMelonfo
odWater20MelonfoodPineapple
8
List.aspx

• ltHTMLgt
• ltscript runatservergt
• private sub foodlist()
• Dim food As String
• If Request.Params.GetValues("food") Is Nothing
  Then
• Response.Write("None of the foods have been
  chosen!" "ltBRgt")
• Else
• For Each food In Request.Params.GetValues("foo
  d")
• Response.Write(food "ltBRgt")
• Next
• End If
• End Sub
• lt/scriptgt
• ltbodygt
• lt foodlist() gt
• lt/bodygt
• lt/HTMLgt

9
foodform.aspx

• lthtmlgtltheadgtlttitlegtFoodlt/titlegtlt/headgt
• ltbodygt
• ltform method"GET" action"list.aspx"gt
• ltpgtltselect size"3" name"food" multiplegt
• ltoptiongtApplelt/optiongt
• ltoptiongtBreadlt/optiongt
• ltoptiongtPineapplelt/optiongt
• ltoptiongtOrangelt/optiongt
• ltoptiongtRicelt/optiongt
• lt/selectgtlt/pgt
• ltpgt
• ltinput type"submit" value"Submit"gt
• ltinput type"reset" value"Reset"gtlt/pgt
• lt/formgt
• lta href'computer.aspx?idltServer.URLEncode("app
  le computer")gt'gt
• I like apple computer lt/agtltbrgt
• lta href"computer.aspx?idIntel computer"gtI like
  Intel computer lt/agt
• lt/bodygtlt/htmlgt

10
computer.aspx

• lthtmlgtltheadgtlttitlegt Computer lt/titlegtlt/headgt
• ltbodygt
• lt "The computer that you like "
  Request.querystring("ID") gt
• lt/bodygtlt/htmlgt

11
Request.Params

• Gets a combined collection of QueryString, Form,
  ServerVariables, and Cookies items.
• Request.Params.Get("name")
• Gets the values of a specified entry in the
  NameValueCollection combined into one
  comma-separated list.
• A String is return.
• Request.Params.GetValues("name")
• Gets the values of a specified entry in the
  NameValueCollection.
• An array of String is returned.

12
Hypertext Links and Forms

• Hypertext link
• lta href"URL?x3yHello"gtNextlt/agt
• Forms
• ltform action"URL" method"post"gt
• Form elements
• lt/formgt

QueryString
Post Send form data as standard input Get Send
form data as QueryString

• URL of the form handling page.
• The default action is to submit to the form
  itself, a common practice in ASP.NET.

13
Variable Name

• Web forms submitting form data via PostBack use
  the form elements id attribute's values as
  identifiers
• You have to use HTML Server Controls or Web
  Server Controls
• E.g., Text1.Text
• Web forms submitting to another ASPX page where
  form elements' name attribute's values are used
  as identifiers.
• Post method Request.Form("x")
• Get method Request.QueryString("x")
• Both Post and Get
• Single value
• Request.Params.Get("x") return a string
• Multiple values
• Request.Params.GetValues("x") return an array
  of strings
• Request.Params.Get("x") Get the values of a
  specified entry in the NameValueCollection
  combined into one comma-separated list (string).

14
State Maintenance

• Web (HTTP) uses a stateless protocol.
• Web forms are created and destroyed each time a
  client browser makes a request.
• Because of this characteristic, variables
  declared within a Web form do not retain their
  value after a page is displayed.
• ASP.NET provides different mechanisms to retain
  data on a Web form between requests.
• To solve this problem, ASP.NET provides several
  ways to retain variables' values between requests
  depending on the nature and scope of the
  information.

15
Cookie
Set cookie entries
Web Server
Browser Workstation
Return cookie entries
16
cookie.txt at Your Browser'S Root Directory

• Netscape HTTP Cookie File
• http//www.netscape.com/newsref/std/cookie_spec.
  html
• This is a generated file! Do not edit.
• 207.67.128.9 FALSE /cgi-bin/ads/ FALS
  E 942189160 code 00L
• iisa.microsoft.com FALSE /iis3 FALSE 946627200 NEW
  VISITOR N
• .netscape.com TRUE / FALSE 946684799 NETSCAPE_ID 0
  00e010,100d11a9
• ad.doubleclick.net FALSE / FALSE 942191940 IAF cb3
  254
• www.allaire.com FALSE / FALSE 2137622400 CFID 1010
  0
• 127.0.0.1 FALSE / FALSE 867761715 BCOLOR GREEN

Name Value
Expiration time of seconds since 1 Jan 1970
Domain Set by client-side script
Secure?
17
State Management Recommendations
ViewState http//msdn.microsoft.com/msdnmag/issue
s/03/02/CuttingEdge/default.aspx
18
ASP Application and Session Objects
I I S
ASP.NET
Application Object 1
Application Object 2
Application Object 3
Session Object 1
Session Object 1
Session Object 1
Session Object 2
Session Object 2
Session Object 2
Session Object 3
Session Object 3
Session Object 3
19
Application Object

• Global.asax is the ASPX file for each application
  resides in the root directory of the application.

An ASP.NET application is the sum of all files,
pages, handlers, modules, and code that reside in
a given virtual directory and its subdirectories
and that users can request through that virtual
directory hierarchy.
20
ASP and Session Management

• Hypertext Transfer Protocol (HTTP) is a stateless
  protocol. Each browser request to a Web server is
  independent, and the server retains no memory of
  a browser's past requests.
• The Session object, one of the intrinsic objects
  supported by ASPX, provides a developer with a
  complete Web session management solution.
• The Session object supports a dynamic associative
  array that a script can use to store information.
  Scalar variables and object references can be
  stored in the session object.
• For each ASPX page requested by a user, the
  Session object will preserve the information
  stored for the user's session. This session
  information is stored in memory on the server.
  The user is provided with a unique session ID
  that ASPX uses to match user requests with the
  information specific to that user's session.

A session is terminated when you close the
browser.
21
Session Object and ViewState Object

• Session ("UserName") "John" ' in page1
• Response.Write(Session("UserName")) ' in page2
• This will store the string "John" in the Session
  object and give it the name "UserName."
• This value can be retrieved from the Session
  object by referencing the Session object by name,
  as in the following
• ViewState("t1") "Test"
• Dim s as String
• S ViewState("t1") ' ViewState("T1") is a
  different variable!
• You can only store a string in a cookie and in a
  ViewState variable.
• The ViewState variable names are case sensitive.
  
• See Online Help on "Saving Web Forms Page Values
  Using View State"

22
Store Objects as Session Variables in the Session
Object

• You may want to use CType() function to cast
  session variable back to an appropriate object
  before you use it.
• In page1.asx
• Dim x1 as New ClassX()
• Session("sv_x") x1
• In page2.aspx
• Dim x2 as New ClassX()
• x2 CType(Session("sv_x"), ClassX)

23
Using Session Objects

• You can use the Session object to store
  information needed for a particular user-session.
  
• Variables stored in the Session object are not
  discarded when the user jumps between pages in
  the application instead, these variables persist
  for the entire user-session.
• The Web server automatically creates a Session
  object when a Web page from the application is
  requested by a user who does not already have a
  session.
• The server destroys the Session object when the
  session expires or is abandoned.
• One common use for the Session object is to store
  user preferences.

24
Session Variables

• Logon.aspx

Session2.aspx
25
Logon.aspx

• lt_at_ Page Language"vb" AutoEventWireup"false"
• Codebehind"logon.aspx.vb" Inherits"exstate.Log
  on"gt
• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• ltHTMLgt
• ltHEADgtlttitlegtsession1lt/titlegtlt/HEADgt
• ltbodygt
• ltform id"Form1" method"post"
  runat"server"gt
• ltPgtUser name
• ltaspTextBox id"TextBoxUserID"
  runat"server"gtlt/aspTextBoxgtlt/Pgt
• ltPgtPassword
• ltaspTextBox id"TextBoxPassword"
  runat"server" TextMode"Password"gt
  lt/aspTextBoxgtlt/Pgt
• ltPgtFirst name
• ltaspTextBox id"TextBoxFirst"
  runat"server"gtlt/aspTextBoxgtlt/Pgt
• ltPgtLast Name
• ltaspTextBox id"TextBoxLast"
  runat"server"gtlt/aspTextBoxgtlt/Pgt
• ltPgtltaspButton id"Button1"
  runat"server" Text"Submit"gtlt/aspButtongtlt/Pgt
• ltPgtltaspLabel id"LabelMsg"
  runat"server"gtlt/aspLabelgtlt/Pgt
• lt/formgt
• lt/bodygt

26
Logon.aspx.vb

• Public Class Logon
• Inherits System.Web.UI.Page
• Protected WithEvents TextBoxUserID As
  System.Web.UI.WebControls.TextBox
• Protected WithEvents TextBoxFirst As
  System.Web.UI.WebControls.TextBox
• Protected WithEvents TextBoxLast As
  System.Web.UI.WebControls.TextBox
• Protected WithEvents Button1 As
  System.Web.UI.WebControls.Button
• Protected WithEvents LabelMsg As
  System.Web.UI.WebControls.Label
• Protected WithEvents TextBoxPassword As
  System.Web.UI.WebControls.TextBox
• Region " Web Form Designer Generated Code "
• '
• End Region
• Private Sub Page_Load(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles MyBase.Load
• LabelMsg.Text "" ' Reset Message
• If Not IsPostBack Then
• If Request.Params.Get("msg")
  "userid" Then
• LabelMsg.Text "Please login
  before you visit other pages on this site."
• End If
• End If
• End Sub

27
Continued

• Private Sub Button1_Click (ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles Button1.Click
• Dim NewUser As New User()
• If TextBoxUserID.Text ltgt "" Then
• If Check(TextBoxUserID.Text,
  TextBoxPassword.Text) Then
• Session("UserID")
  TextBoxUserID.Text
• NewUser.FirstName
  TextBoxFirst.Text
• NewUser.LastName
  TextBoxLast.Text
• Session("UserName") NewUser
• Response.Redirect("session2.aspx")
  
• Else
• LabelMsg.Text "Your user id and
  password does not match what is in our file"
• End If
• Else
• LabelMsg.Text "You need to enter
  your user id"
• End If
• End Sub
• Private Function Check(ByVal user As String,
  ByVal pswd As String) As Boolean
• If user pswd Then

28
User Class

• Public Class User
• Public FirstName As String
• Public LastName As String
• End Class

29
Sesison2.aspx

• lt_at_ Page Language"vb" AutoEventWireup"false"
• Codebehind"Session2.aspx.vb" Inherits"exstate.S
  ession2"gt
• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• ltHTMLgt
• ltHEADgt
• lttitlegtSession2lt/titlegt
• lt/HEADgt
• ltbodygt
• ltform id"Form1" method"post"
  runat"server"gt
• ltPgtHi
• ltaspLabel id"LabelFirstName"
  runat"server"gtlt/aspLabelgt
• ltaspLabel id"LabelLastName"
  runat"server"gt lt/aspLabelgtlt/Pgt
• ltPgtYour User ID is
• ltaspLabel id"LabelUserID"
  runat"server"gtlt/aspLabelgtlt/Pgt
• lt/formgt
• lt/bodygt
• lt/HTMLgt

30
Session2.aspx.vb

• Public Class Session2
• Inherits System.Web.UI.Page
• Protected WithEvents LabelFirstName As
  System.Web.UI.WebControls.Label
• Protected WithEvents LabelLastName As
  System.Web.UI.WebControls.Label
• Protected WithEvents LabelUserID As
  System.Web.UI.WebControls.Label
• Region " Web Form Designer Generated Code "
• ' ..
• End Region
• Private Sub Page_Load (ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles MyBase.Load
• LabelUserID.Text Session("UserID")
• Dim CurrentUser As New User()
• If Session("UserName") Is Nothing Then
• Response.Redirect("Logon.aspx?msguser
  id")
• Else
• CurrentUser CType(Session("UserName"
  ), User)
• LabelFirstName.Text
  CurrentUser.FirstName
• LabelLastName.Text
  CurrentUser.LastName
• End If
• End Sub

31
Dynamic Web Site for EC
Session ID
Session Variables
http//etail.com/shop.aspx?
lt session("Name1") session("Name2") gt lt
While (dr.Next()) gt ltpgtltPRODgt lt
dw.getString("Product") gt lt/PRODgtlt/Pgt
lt End While gt
Source Adapted from Technology Forecast 2000.
PriceWaterhouseCoopers.
32
WebForm1.aspx
End the session and then submit again!
33
WebForm1.aspx

• lt_at_ Page Language"vb" AutoEventWireup"false"
• Codebehind"WebForm1.aspx.vb"
  Inherits"state.WebForm1"gt
• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• ltHTMLgt
• ltHEADgt
• lttitlegtWebForm1lt/titlegt
• ltmeta content"Microsoft Visual
  Studio.NET 7.0" name"GENERATOR"gt
• ltmeta content"Visual Basic 7.0"
  name"CODE_LANGUAGE"gt
• ltmeta content"JavaScript"
  name"vs_defaultClientScript"gt
• ltmeta content"http//schemas.microsoft.co
  m/intellisense/ie5" name"vs_targetSchema"gt
• lt/HEADgt
• ltbodygt
• ltform id"Form1" method"post" runat"server"gt
• ltPgtViewState ltasptextbox
  id"TextBoxViewState" runat"server"gtlt/asptextbox
  gtlt/Pgt
• ltPgtCookie ltasptextbox id"TextBoxCookie"
  runat"server"gtlt/asptextboxgtlt/Pgt
• ltPgtSession ltasptextbox id"TextBoxSession"
  runat"server"gtlt/asptextboxgtlt/Pgt
• ltPgtApplication ltasptextbox
  id"TextBoxApplication" runat"server"gt
• lt/asptextboxgtlt/Pgt
• ltPgtltaspbutton id"ButtonSubmit"
  runat"server" Text"Submit!"gt

34
WebForm1.aspx.vb

• Public Class WebForm1
• Inherits System.Web.UI.Page
• Protected WithEvents TextBoxViewState As
  System.Web.UI.WebControls.TextBox
• Protected WithEvents TextBoxCookie As
  System.Web.UI.WebControls.TextBox
• Protected WithEvents TextBoxSession As
  System.Web.UI.WebControls.TextBox
• Protected WithEvents TextBoxApplication As
  System.Web.UI.WebControls.TextBox
• Protected WithEvents ButtonSubmit As
  System.Web.UI.WebControls.Button
• Protected WithEvents ButtonEndSession As
  System.Web.UI.WebControls.Button
• Protected WithEvents ButtonGoWebForm2 As
  System.Web.UI.WebControls.Button
• Protected WithEvents Label1 As
  System.Web.UI.WebControls.Label

35
Continued

• Private Sub ButtonSubmit_Click(ByVal sender As
  System.Object,
• ByVal e As System.EventArgs) Handles
  ButtonSubmit.Click
• If ViewState("vs1") Is Nothing Then '
  Check existence
• Label1.Text "ViewState variable
  Nothing"
• Else
• Label1.Text "ViewState variable "
  ViewState("vs1")
• End If
• ViewState("vs1") TextBoxViewState.Text
• If Request.Browser.Cookies Then '
  Browser support cookie
• If Request.Cookies("cookie1") Is
  Nothing Then
• Label1.Text "ltbrgtCookie
  variable Nothing"
• Else
• Label1.Text "ltbrgtCookie
  variable " Request.Cookies("cookie1").Value
• End If
• ' Create a cookie.
• Dim ck1 As New HttpCookie("cookie1")
• ck1.Value TextBoxCookie.Text
• ck1.Expires Now.AddDays(1)
• ' Add the cookie.

36
Continued

• If Session.IsNewSession Then
• Label1.Text "ltbrgtThis is a new
  session!"
• End If
• If Session("sv1") Is Nothing Then
• Label1.Text "ltbrgtSession variable
  Nothing"
• Else
• Label1.Text "ltbrgtSession variable
  " Session("sv1")
• Label1.Text "ltbrgtSession ID "
  Session.SessionID.ToString()
• Label1.Text "ltbrgtSession Timeout
  " Session.Timeout
• End If
• Session("sv1") TextBoxSession.Text
• If Application("av1") Is Nothing Then
• Label1.Text "ltbrgtApplication
  variable Nothing"
• Else
• Label1.Text "ltbrgtApplication
  variable " Application("av1")
• End If
• Application("av1") TextBoxApplication.Te
  xt

37
Continued

• Private Sub ButtonEndSession_Click(ByVal sender
  As System.Object,
• ByVal e As System.EventArgs) Handles
  ButtonEndSession.Click
• Session.Abandon()
• ' Session.RemoveAll()
• End Sub
• Private Sub ButtonGoWebForm2_Click(ByVal sender
  As System.Object,
• ByVal e As System.EventArgs) Handles
  ButtonGoWebForm2.Click
• Dim x1 As New ClassX()
• Session("sv_x1") x1
• Response.Redirect("WebForm2.aspx")
• End Sub
• End Class

38
Global.asax

• Imports System.Web
• Imports System.Web.SessionState
• Public Class Global
• Inherits System.Web.HttpApplication
• Region " Component Designer Generated Code "
• ..
• End Region
• Sub Application_Start(ByVal sender As Object,
  ByVal e As EventArgs)
• ' Fires when the application is started
• End Sub
• Sub Session_Start(ByVal sender As Object,
  ByVal e As EventArgs)
• ' Fires when the session is started
• ' Response.Redirect("Login.aspx")
• Application.Lock()
• If Application("ConurrentSession") Is
  Nothing Then
• Application("ConurrentSession") 0
• End If
• Application("ConurrentSession") 1
• Application.UnLock()

39
Continued

• Sub Application_BeginRequest(ByVal sender As
  Object, ByVal e As EventArgs)
• ' Fires at the beginning of each request
• End Sub
• Sub Application_AuthenticateRequest(ByVal
  sender As Object, ByVal e As EventArgs)
• ' Fires upon attempting to authenticate
  the use
• End Sub
• Sub Application_Error(ByVal sender As Object,
  ByVal e As EventArgs)
• ' Fires when an error occurs
• End Sub
• Sub Session_End(ByVal sender As Object, ByVal
  e As EventArgs)
• ' Fires when the session ends
• Application.Lock()
• If Application("ConurrentSession") Is
  Nothing Then
• Application("ConurrentSession") 0
• End If
• Application("ConurrentSession") - 1
• Application.UnLock()
• End Sub
• Sub Application_End(ByVal sender As Object,
  ByVal e As EventArgs)

40
The Disadvantages of Using Cookies

• Limited size. Most browsers place a 4096-byte
  limit on the size of a cookie, although the
  support for 8192-byte cookie size is becoming
  common in the new browser and client-device
  versions available today.
• User-configured refusal. Some users disable their
  browser or client device's ability to receive
  cookies, thereby limiting this functionality.
• Security. Cookies are subject to tampering. Users
  can manipulate cookies on their computer, which
  can potentially represent a security compromise
  or cause the application dependent on the cookie
  to fail.
• Durability. The durability of the cookie on a
  client computer is subject to cookie expiration
  processes on the client and user intervention.
• Cookies are often used for personalization, where
  content is customized for a known user. In most
  of these cases, identification is the issue
  rather than authentication, so it is enough to
  merely store the user name, account name, or a
  unique user ID (such as a GUID) in a cookie and
  use it to access the user personalization profile
  from a database of the site.

41
Cookieless Session
Web.config

• InProc
• StateServer
• SQLServer

• ltconfigurationgt
• ltsystem.webgt
• ltsessionState
• mode"InProc"
• stateConnectionString"tcpip127.0.0.142424
  "
• sqlConnectionString"data
  source127.0.0.1user idsapassword"
• cookieless"true"
• timeout"20"
• /gt
• lt/configurationgt
• lt/system.webgt

Default value is false

• All the URL to pages in the web site must use
  document relative URLs.
• You cannot use absolute URLs or root relative
  URLs,
• such as lta href"/abc/page1.aspx"gtTestlt/agt

42

• Source
• http//www.fawcette.com/dotnetmag/2002_10/online/b
  olges/default_pf.asp

43
Cookieless Session
44
Variables Scope
Type Retrieval Creation Scope
Form Request.Form Request.Params.Get Request.Params.GetValues Form Post Method or PostBack HTML form elements Web Server Controls HTML Server Controls Current form via Postback Action page
URL Request.QueryString Request.Params.Get Request.Params.GetValues Query string of URL Form elements (Get Method) Hyperlinked or targeted page
Cookie Request.Cookies("x") Dim ck1 As New HttpCookie("x") ck1.Value TextBoxCookie.Text ck1.Expires Now.AddDays(1) Response.Cookies.Add(ck1) Before cookie expired from the same client station
ViewState Viewstate("x") ViewState("x") 1 Same page during PostBack
Session Session("x") Session("x") 1 Same visitor during a session
Application Application("x") Application("x") 1 All pages from the same site!