IAD LAB-6: VIEWSTATE
Problem Statement:
Problem 1
Implement a simple program that uses viewstate to store and retrieve counter value.
Whenever Increment button is clicked counter should be incremented by 2. Write code behind below.
If this page is accessed using different browser windows, or from more than one clients,
whether the counter value would be same, or it would be different at different time instants?
Give reason for the observation.
Problem 2
Extend the program implemented above and make the View State secure.
Refer to the textbook for the technique of securing.
Problem 3
Consider the following definition of customer class. Develop a web form that stores
three objects of customer in viewstate. Implement the code for retrieving customer objects also.
Code Implementation
Unencrypted Viewstate
Partial Class Counter
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
' Set default counter to 0 if first time loading
If Not IsPostBack Then
ViewState("Counter") = 0
lblCounter.Text = "Counter: 0"
End If
End Sub
Protected Sub btnIncrement_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnIncrement.Click
Dim count As Integer = CType(ViewState("Counter"), Integer)
count += 2
ViewState("Counter") = count
lblCounter.Text = "Counter: " & count.ToString()
End Sub
End Class
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="Counter" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Simple Counter</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<h2>TASK 1: Viewstate Without Encryption</h2>
<h2>Click to increase the counter by 2</h2>
<asp:Label ID="lblCounter" runat="server" Text="Counter: 0" Font-Size="Large"></asp:Label><br /><br />
<asp:Button ID="btnIncrement" runat="server" Text="Increment" />
</div>
<br><br><br><br><br><br>
<div>
<h2>TASK 2: Viewstate With Encryption</h2>
<a href="EncryptedViewstate.aspx">Visit Encrypted Viewstate</a><br />
<h2>TASK 3: Serialization Class</h2>
<a href="seiralization.aspx">Visit Class Serialization</a>
</div>
</form>
</body>
</html>
Encrypted Viewstate
Partial Class Default2
Inherits System.Web.UI.Page
Private Sub Default2_Load(sender As Object, e As EventArgs) Handles Me.Load
If Not IsPostBack Then
ViewState("Counter") = 0
lblCounter.Text = "Counter: 0"
End If
End Sub
Private Sub btnIncrement_Click(sender As Object, e As EventArgs) Handles btnIncrement.Click
Dim count As Integer = CType(ViewState("Counter"), Integer)
count += 2
ViewState("Counter") = count
lblCounter.Text = "Counter: " & count
End Sub
End Class
<%@ Page Language="VB" ViewStateEncryptionMode="Always" AutoEventWireup="false" CodeFile="EncryptedViewstate.aspx.vb" Inherits="Default2" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<h2>Encrypted Viwestate Counter Value</h2>
<asp:Label ID="lblCounter" runat="server" Text="Counter: 0"></asp:Label>
<br />
<br />
<asp:Button ID="btnIncrement" runat="server" Text="Increment" />
<br />
<br />
<br />
</div>
</form>
</body>
</html> 
Class Serialization
Partial Class Default2
Inherits System.Web.UI.Page
Protected Sub btnSubmitCustomer_Click(sender As Object, e As EventArgs) Handles btnSubmitCustomer.Click
Dim first As String = txtFirstName.Value
Dim last As String = txtLastName.Value
Dim cust As New Customer(first, last)
Dim customers As List(Of Customer)
If ViewState("CurrentCustomer") IsNot Nothing Then
customers = CType(ViewState("CurrentCustomer"), List(Of Customer))
Else
customers = New List(Of Customer)
End If
customers.Add(cust)
ViewState("CurrentCustomer") = customers
lblsubmitted.Text = "The Customer " & first & " " & last & " has been Submitted Successfully!"
End Sub
Protected Sub btnRetrieveCustomer_Click(sender As Object, e As EventArgs) Handles btnRetrieveCustomer.Click
If ViewState IsNot Nothing Then
lblCustomers.Text = ""
Dim customers As List(Of Customer) = CType(ViewState("CurrentCustomer"), List(Of Customer))
For Each cust As Customer In customers
lblCustomers.Text &= cust.FirstName & " " & cust.LastName & "<br />"
Next
End If
End Sub
End Class
<Serializable()>
Public Class Customer
Private _firstName As String
Public Property FirstName() As String
Get
Return _firstName
End Get
Set(ByVal Value As String)
_firstName = Value
End Set
End Property
Private _lastName As String
Public Property LastName() As String
Get
Return _lastName
End Get
Set(ByVal Value As String)
_lastName = Value
End Set
End Property
Public Sub New(ByVal firstName As String, ByVal lastName As String)
Me.FirstName = firstName
Me.LastName = lastName
End Sub
End Class
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="serialization.aspx.vb" Inherits="Default2" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<br />
<asp:Label ID="lblFirstName" runat="server" Text="First Name"></asp:Label>
<br />
<input id="txtFirstName" type="text" runat="server" /><br />
<br />
<asp:Label ID="lblLastName" runat="server" Text="Last Name"></asp:Label>
<br /><input id="txtLastName" type="text" runat="server"/><br />
<br />
<asp:Button ID="btnSubmitCustomer" runat="server" Text="Submit Customer" Width="160px" />
<br />
<asp:Label ID="lblsubmitted" runat="server"></asp:Label>
<br />
<br />
<asp:Button ID="btnRetrieveCustomer" runat="server" Text="Retrieve Customer" />
<br />
<asp:Label ID="lblCustomers" runat="server"></asp:Label>
<br />
<br />
</div>
</form>
</body>
</html>
Sample Output
TASK 1
The counter value will be different for each browser window or client because ViewState is stored on the client side and is specific to a single page instance. When a user interacts with the page, the ViewState is sent back and forth between the server and that particular client only, making it unique to that session and page. Therefore, multiple users or different browser instances will have their own independent ViewState data, resulting in different counter values at different times.
TASK 2
View state encryption can be enabled either for an individual page using the ViewStateEncryptionMode attribute in the Page directive, or globally for all pages through the configuration file by setting <pages viewStateEncryptionMode="Always" /> inside <system.web>. This ensures that the view state is always encrypted. The available settings are Always, Never, and Auto. By default, it is set to Auto, which means view state is only encrypted if a specific control on the page requires it.
TASK 3
In ASP.NET, custom objects can be stored in view state, but they must be serializable, meaning they need to be converted into bytes. If the object is not serializable, an error will occur. To make it serializable, the [Serializable] attribute must be added to the class.
