Using ViewState

I'm trying to learn to use ViewState but I guess I'm a little confuse. On a logon page, I have the following:

Code:

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Dim vsViewState As classData.vsInfo (vsInfo is a serializable struture)

Protected Sub Page_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
        Me.ViewState.Add("ViewStateData", vsViewState)
    End Sub

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When you user enter their username/password and choose a session that they logon, I define the following:

Code:

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    Protected Sub btnLogon_Click(ByVal sender As Object, ByVal e As System.EventArgs)

                vsViewState.Username = getUserName()
                vsViewState.Password = getPassword()
                vsViewState.GroupID = getGroupID()
End Sub

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After the user logon, I want to display the username/pass & the group that they login on the next page:

Code:

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Dim vsViewState As classData.vsInfo (vsInfo is a serializable struture)

Protected Sub Page_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
        Me.ViewState.Add("ViewStateData", vsViewState)
    End Sub

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Code:

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Public ReadOnly Property ViewStateInfo() As classData.vsInfo
        Get
            Dim vsValues As classData.vsInfo
            vsValues = CType(ViewState("ViewStateData"), classData.vsInfo)
            Return vsInfo
        End Get
    End Property

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Code:

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Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
                Dim groupID As String = ViewStateInfo.GroupID
                Dim username As String = ViewStateInfo.Username
    End Sub

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My groupID & username is nothing...do you know why?

If you want to store custom objects in the ViewState or ControlState you have to override the appropriate methods on the page.

So for ViewState you would need to override LoadViewState and SaveViewState. Make sure you still use the base versions of those methods as well to avoid losing any data other controls are saving to the ViewState.

I'm not sure how it works with the methods you are using. I prefer to just override the methods and work directly with the object.

However I would HIGHLY recommend against storing any sensative data, especially passwords, in the ViewState. Passwords should be taken to the server, hashed and compared and nothing more.

Use a session variable to hold a user ID or user name. Read that on all the other pages or on the same page itself. You don't need to keep posting it back in viewstate.

I have a problem using session variable before, after writing to a file, my session variables are no longer there. This is why I'm thinking of using viewstate. Anything else you would recommend? What are the reasons that could cause lost of variables in session?
Thanks!

Show the code that you tried to use. How you set it, how you read it.

First of all, thanks for willing to take a look at this:

This is what I have on the logon page when user click logon, the following session variables are retrieved:

Code:

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    Protected Sub btnLogon_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        Try
            Dim clsRData As New clsRData
            Dim clsACData As New clsACData
            Dim clsRSum As New clsRSummary
            If (clsRData.ValidateUser(getUserName, getPassword, getGroupID)) Then
                Session("username") = getUserName()
                Session("password") = getPassword()
                Session("groupID") = getGroupID()
                Session("groupIDwName") = getGroupIDwName()
                Session("recruiterID") = clsRSum.getLoginRecruiterID(getUserName())
                Session("OpCloseInd") = getOpCloseInd()
                Session("logonYear") = Left(getLogonYear(), 4)
                Session.Timeout = 240
                Response.Redirect("~\ACStart.aspx")
            Else
                UpdatePanel2.Visible = "true"
                lblPassError.Text = "Invalid Password, please try again."

            End If
        Catch ex As Exception
            Throw
        End Try
    End Sub

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Once user logon, they could go to any of the listed pages. One of the pages involve assigning the tables to various people in the database. The tables data come from 4 text files so I endedup combine the 4 textfiles and have an Open/Close indicator to mark whether the table is assigned. Thus, after the table is assigned, the text file is rewrite. The following is the button_submit click on table assigning page.

Code:

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Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click
        Dim clsACData As New clsACData
        Dim clsRData As New clsRData
        Dim groupID As String = Session("groupID")
        groupID = Trim(groupID)
        Dim retreatDate As String = clsRData.RetreatDate(groupID)
        retreatDate = Replace(retreatDate, "/", "")

        Dim path As String = My.Request.PhysicalApplicationPath & "App_Code\" & groupID & "_" & retreatDate & "\" & "tempTable1_10.txt"
        Dim path2 As String = My.Request.PhysicalApplicationPath & "App_Code\" & groupID & "_" & retreatDate & "\" & "tempTable11_20.txt"
        Dim path3 As String = My.Request.PhysicalApplicationPath & "App_Code\" & groupID & "_" & retreatDate & "\" & "tempTable21_30.txt"
        Dim path4 As String = My.Request.PhysicalApplicationPath & "App_Code\" & groupID & "_" & retreatDate & "\" & "tempTable31_42.txt"

        Dim assignStr, assignStr2, assignStr3, assignstr4 As String()
        If File.Exists(path) Then
            assignStr = clsRData.GetListOfTempAssignsNoSkip("tempTable1_10", groupID)
        Else
            assignStr = clsRData.GetListOfAssignsNoSkip("Table1_10")
        End If

        If File.Exists(path2) Then
            assignStr2 = clsRData.GetListOfTempAssignsNoSkip("tempTable11_20", groupID)
        Else
            assignStr2 = clsRData.GetListOfAssignsNoSkip("Table11_20")
        End If

        If File.Exists(path3) Then
            assignStr3 = clsRData.GetListOfTempAssignsNoSkip("tempTable21_30", groupID)
        Else
            assignStr3 = clsRData.GetListOfAssignsNoSkip("Table21_30")

        End If
        If File.Exists(path4) Then
            assignstr4 = clsRData.GetListOfTempAssignsNoSkip("tempTable31_42", groupID)
        Else
            assignstr4 = clsRData.GetListOfAssignsNoSkip("Table31_42")
        End If

        Dim tempAssignStr As String() = clsRData.JoinArrays(assignStr, assignStr2)
        Dim tempAssignStr2 As String() = clsRData.JoinArrays(assignStr3, assignstr4)
        Dim finalAssignStr As String() = clsRData.JoinArrays(tempAssignStr, tempAssignStr2)

        'Existing TableList in database
        Dim assignedTables As String()
        assignedTables = clsRData.RetrieveAssignedTables(groupID)

        Dim attempAssignedTables(GridView1.Rows.Count) As String
        For Each gvr As GridViewRow In GridView1.Rows
            'Get a programmatic reference to the TextBox control
            Dim inputStr As String = CType(gvr.FindControl("TableNumber"), TextBox).Text
            Dim recordIDStr As String = CType(gvr.FindControl("RetreatantID"), Label).Text
            Dim tableIDStr As String = CType(gvr.FindControl("TableID"), Label).Text

            'check input values against exiting values in db
            Dim compareFlag As Integer
            For m As Integer = 0 To assignedTables.Length - 1
                compareFlag = String.Compare(assignedTables(m), inputStr)
                If (compareFlag = 0) Then
                    m = assignedTables.Length - 1
                End If
            Next m
            If (compareFlag = 0) Then
                lblError3.Text = "One or more tables already assigned to a retreatant. Please re-run your retreatant list not assigned a table to designate a new table."
                'check existing values agains text file & mark it closed if still avail
                For k As Integer = 0 To assignedTables.Length - 1
                    For l As Integer = 0 To finalAssignStr.Length - 1
                        Dim compareFlag2 As String
                        compareFlag2 = String.Compare(assignedTables(k), Mid(finalAssignStr(l), 5))
                        If (compareFlag2 = 0) Then
                            finalAssignStr(l) = Replace(finalAssignStr(l), "O", "C")
                        End If
                    Next l
                Next k

            Else
                'update database & mark value unavail
                clsACData.UpdateTableAssign(recordIDStr, inputStr, tableIDStr)
                For n As Integer = 0 To finalAssignStr.Length - 1
                    If String.Compare(Right(finalAssignStr(n), finalAssignStr(n).Length - 4), inputStr) = 0 Then
                        finalAssignStr(n) = Replace(finalAssignStr(n), "O", "C")
                    End If
                Next
            End If
        Next

        clsRData.ReWriteTableList(finalAssignStr, groupID)

        btnAutoAssign.Visible = "false"
        btnCancel.Visible = "false"
        btnSubmit.Visible = "false"
        GridView1.Visible = False

        ListBox1.DataSource = New String() {}
        ListBox1.DataBind()
        ListBox1.DataSource = clsRData.GetListOfTempAssigns("tempTable1_10", groupID)
        ListBox1.DataBind()

        ListBox2.DataSource = New String() {}
        ListBox2.DataBind()
        ListBox2.DataSource = clsRData.GetListOfTempAssigns("tempTable11_20", groupID)
        ListBox2.DataBind()

        ListBox3.DataSource = New String() {}
        ListBox3.DataBind()
        ListBox3.DataSource = clsRData.GetListOfTempAssigns("tempTable21_30", groupID)
        ListBox3.DataBind()

        ListBox4.DataSource = New String() {}
        ListBox4.DataBind()
        ListBox4.DataSource = clsRData.GetListOfTempAssigns("tempTable31_42", groupID)
        ListBox4.DataBind()

    End Sub

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Everything looks just fine...except after I submit the tables assigned and attempt to go to another page, all my session values that stored from the logon page is lost. Any idea? I know it's hard to predict at this point, but anything is appreciated. Thanks!