session variable loses value after detailsview new cancel event - asp.net

Question

I have 3 controls on my web page, a dropdownlist, a detailsview, and a listview.
the dropdownlist controls the record to be displayed on the detailsview and the listview.
when the detailsview enters "new" mode I clear the items of the detailsview and clear the values of the dropdownlist:
If e.CommandName = "New" Then
lvRecipeSteps.Items.Clear()
ddRecipeItemNumber.Items.Clear()
End If
this shows the page with no items on the dropdownlist, the detailsview and listview on new/insert mode.
the issue happens when I click the cancel event, then this code is executed
If e.CommandName = "Cancel" Then
ddRecipeItemNumber.DataBind()
ddRecipeItemNumber.SelectedValue = Session("Id").ToString()
End If
the session variable Id gets assign on page load
Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load
Session("Id") = ddRecipeItemNumber.SelectedValue
I get an error: "not set to an instance of an object" pointing to: ddRecipeItemNumber.SelectedValue = Session("Id").ToString()
I want to be able to save the record Id, that is on the dropdown before the new/insert event begins, and then if the event gets cancelled, set the controls back to the record that were displaying before the insert/new action started.
I read that using sessions variables is a good way of doing this, but I most be doing something wrong that when the event cancel is executed, the values is then lost.
Please let me know if I can get some help finding a solution for my problem.
Thank you very much.

Answer 1

place the Session("Id") = ddRecipeItemNumber.SelectedValue inside the condition below:
if (!IsPostBack)
{
Session("Id") = ddRecipeItemNumber.SelectedValue;
}
just need to convert it to VB
UPDATE 1
If your code is not inside a Data control then you could allocate its selected value like the code below:
on your aspx form:
<asp:DropDownList ID="DropDownList2" runat="server"
OnSelectedIndexChanged="DropDownList2_SelectedIndexChanged"
AutoPostBack="true" ></asp:DropDownList>
on your code behind:
protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
{
Session["Id"] = DropDownList2.SelectedItem.Value;
}
UPDATE 2
also if you want to change the selected value on your code this would be the right code to do:
instead of this line ddRecipeItemNumber.SelectedValue = Session("Id").ToString()
use this one
ddRecipeItemNumber.Items.FindByValue(Session("Id").ToString()).Selected = true;