Lab 05 - Employee Payroll Portal

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

Problem-1:

1.Counter.aspx

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Counter.aspx.vb" Inherits="Counter" %>

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Counter Using ViewState</title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <asp:Label ID="lblCounter" runat="server" Font-Size="Large" Text="Counter: 0"></asp:Label>
            <br /><br />
            <asp:Button ID="btnIncrement" runat="server" Text="Increment by 2" OnClick="btnIncrement_Click" />
        </div>
    </form>
</body>
</html>

2.Counter.vb

 Partial Class Counter
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not IsPostBack Then
            ViewState("counter") = 0
        End If
        lblCounter.Text = "Counter: " & ViewState("counter").ToString()
    End Sub

    Protected Sub btnIncrement_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        Dim count As Integer = CInt(ViewState("counter"))
        count += 2
        ViewState("counter") = count
        lblCounter.Text = "Counter: " & count.ToString()
    End Sub
End Class

Problem-2:

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Counter.aspx.vb" Inherits="Counter" ViewStateEncryptionMode="Always" %>

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Counter Using ViewState (Encrypted)</title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <asp:Label ID="lblCounter" runat="server" Font-Size="Large" Text="Counter: 0"></asp:Label>
            <br /><br />
            <asp:Button ID="btnIncrement" runat="server" Text="Increment by 2" OnClick="btnIncrement_Click" />
        </div>
    </form>
</body>
</html>

Problem-3:

3. Customer.vb

<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

4. Default.aspx(cutomer retrievel)

 <%@ Page Language="VB" AutoEventWireup="true" CodeFile="Default.aspx.vb" Inherits="_Default" %>

<!DOCTYPE html>
<html>
<head>
    <title>Customer ViewState Demo</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:Button ID="btnStoreCustomers" runat="server" Text="Store Customers" OnClick="btnStoreCustomers_Click" />
        <asp:Button ID="btnRetrieveCustomers" runat="server" Text="Retrieve Customers" OnClick="btnRetrieveCustomers_Click" />
        <br /><br />
        <asp:Literal ID="litOutput" runat="server" />
    </form>
</body>
</html>

5. Default.vb(cutomer retrievel)

 Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub btnStoreCustomers_Click(sender As Object, e As EventArgs)
        ' Create customer instances
        Dim cust1 As New Customer("Areeba", "Khan")
        Dim cust2 As New Customer("Bilal", "Nadeem")
        Dim cust3 As New Customer("Farah", "Iqbal")

        ' Add to list
        Dim customers As New List(Of Customer)
        customers.Add(cust1)
        customers.Add(cust2)
        customers.Add(cust3)

        ' Store in ViewState
        ViewState("CustomerList") = customers

        litOutput.Text = "<b>3 Customers stored successfully in ViewState.</b>"
    End Sub

    Protected Sub btnRetrieveCustomers_Click(sender As Object, e As EventArgs)
        ' Retrieve from ViewState
        Dim customers As List(Of Customer) = TryCast(ViewState("CustomerList"), List(Of Customer))

        If customers IsNot Nothing Then
            Dim result As String = "<b>Retrieved Customers:</b><ul>"
            For Each cust As Customer In customers
                result &= "<li>" & Server.HtmlEncode(cust.FirstName & " " & cust.LastName) & "</li>"
            Next
            result &= "</ul>"
            litOutput.Text = result
        Else
            litOutput.Text = "<b>No customer data found in ViewState.</b>"
        End If
    End Sub
End Class

Sample Outputs

Problem-1

Problem-2

Problem-3

Demonstration