Button Stops Functioning when Trying to Assign Session Variable - asp.net

Question

I am trying to retain a list of strings after a button press and have been using session variables. This is a snippet of the code:
.aspx page
<asp:Panel runat="server" ID="pnlAdd" >
<asp:DropDownList runat="server" ID="ddlOrder" >
<asp:ListItem Value="-1">Select an Order Type</asp:ListItem>
<asp:ListItem Value="1">hey there</asp:ListItem>
</asp:DropDownList>
<asp:DropDownList runat="server" ID="ddlOrderStatus" >
<asp:ListItem Value="-1">Select an Order Status</asp:ListItem>
<asp:ListItem Value="1">another option</asp:ListItem>
</asp:DropDownList>
</asp:Panel>
<br />
<asp:Button runat="server" ID="btnAdd" Text="Add" />
.vb page
Protected Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
Dim list As New List(Of String)
list = Session("flist")
list.Add(ddlOrder.SelectedItem.Text + " " + ddlOrderStatus.SelectedItem.Text)
Session("flist") = list
For i As Integer = 0 To 10
MsgBox(i.ToString + " " + list(i))
Next
MsgBox("Here")
End Sub
At the point that I assign the Session variable to list with list = Session("flist"), nothing will happen on the button click. If I remove that line, the rest of the button fires. Am I using the Session variable incorrectly? How can I achieve this correctly?

Answer 1

The list (of String) cannot be nothing before you are going to add elements into this list, So, change your code as follows:
Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
Dim list As New List(Of String)
Dim objList As Object = Session.Item("flist")
If objList IsNot Nothing AndAlso TypeOf (objList) Is List(Of String) Then
list = CType(objList, List(Of String))
End If
list.Add(ddlOrder.SelectedItem.Text + " " + ddlOrderStatus.SelectedItem.Text)
Session("flist") = list
For i As Integer = 0 To list.Count - 1
MsgBox(i.ToString + " " + list(i))
Next
MsgBox("Here on end")
End Sub