Keeping a DropDownList's DataSource Updated

The DropDownList does not manage selected state like other controls. Therefore, I use a Session variable to store an index to keep track of the currently selected item:

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            Session["listId"] = ddlList.SelectedValue;
            GridViewStocksInLists.DataBind();
        }
    }

Now, I add the SelectedIndexChanged event with the following code:

    protected void ddlList_SelectedIndexChanged(object sender, EventArgs e)
    {
        Session["listId"] = ddlList.SelectedValue;
        GridViewStocksInLists.DataBind();
    }

Reference: http://www.velocityreviews.com/forums/t123449-problem-with-formview-and-dropdownlists.html