Question

I’m having problems with retrieving multiple instances of a session variable from an InProc session state.

In the following code I persist a simple BusinessObject into a session variable on the Page_Load event. On the click of a button I try to retrieve the object back into 2 new declared instances of the same BusinessObject.

All works great until I change one of the properties in the first instance, it changes the second instance as well.

Is this normal behaviour? I would have thought as these were new instances they wouldn’t demonstrate static behaviour?

Any ideas where I’m going wrong?

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        If Not Page.IsPostBack Then
            ' create a new instance of a business object and set a containg variable
            Dim BO As New BusinessObject
            BO.SomeVariable = "test"
            ' persist to inproc session
            Session("BO") = BO
        End If

    End Sub

    Protected Sub btnRetrieveSessionVariable_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnRetrieveSessionVariable.Click

        ' retrieve the session variable to a new instance of BusinessObject
        Dim BO1 As New BusinessObject
        If Not Session("BO") Is Nothing Then BO1 = Session("BO")

        ' retrieve the session variable to a new instance of BusinessObject
        Dim BO2 As New BusinessObject
        If Not Session("BO") Is Nothing Then BO2 = Session("BO")

        ' change the property value on the first instance
        BO1.SomeVariable = "test2"

        ' why has this changed on both instances?
        Dim strBO1Property As String = BO1.SomeVariable
        Dim strBO2Property As String = BO2.SomeVariable

    End Sub

    ' simple BusinessObject class
    Public Class BusinessObject
        Private _SomeVariable As String

        Public Property SomeVariable() As String
            Get
                Return _SomeVariable
            End Get
            Set(ByVal value As String)
                _SomeVariable = value
            End Set
        End Property
    End Class

Answer 1

your BO1 and BO2 are the same object
BO1 is a name that references some area in memory;
BO2 is another name that references the SAME area of memory; Session(“BO”) references the SAME area of memory.

To truly create different objects BO1 and BO2, you should create a copy of the object – for example implement Clone() method in your business object class.