Using ViewState

[VBnewbeee]

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

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

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

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

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

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

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

 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

 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

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