Dynamically added listbox event is not firing

My problem is when I clicked on one listbox another list box has to come dynamically with related values.... list box is coming but listbox event is not firing....I saw some answers in this website but that answer is not suited for my application can any one please give the answer... Here is a quick code please see the code and give me the answers asap...

Thanks in advance....

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {

            SqlCommand com = new SqlCommand("select EmpId,EmpName from OrgChart where      ManagerID=0", con);
            con.Open();
            SqlDataReader dr = com.ExecuteReader();
           int i=0;

            while (dr.Read())
            {
                empid[i] = Convert.ToInt32(dr[0].ToString());
                ename[i] = dr[1].ToString();
                i++;


            }
            for(int j=0;j<i;j++)
                ListBox1.Items.Add(empid[j]+"-"+ename[j]);

            ListBox1.Items.Add("create new");
        }



    }


    protected void ListBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        Table1.Visible =false;
        Table2.Visible = false;
        string comand = ListBox1.SelectedValue.ToString();
        if (comand == "create new")
        {
            Table1.Visible = true;
        }
        else
        {
            Table2.Visible = true;
            string[] emp = comand.Split('-');
            getdetails(Convert.ToInt32(emp[0]));


        }
    }
    static ListBox lb = new ListBox();           
    void getdetails(int empid)
    {

            managerid = empid;

                con.Open();
            com = new SqlCommand("select EmpId,EmpName from OrgChart where ManagerID=" + managerid + "", con);
            dr = com.ExecuteReader();

            lb.ID = "lb1";
            lb.AutoPostBack = true;


            while (dr.Read())
            {
                lb.Items.Add(dr[0].ToString() + "-" + dr[1].ToString());

            }
            lb.Items.Add("create new");

            lb.SelectedIndexChanged += new EventHandler(this.lb_SelectedIndexChanged);

            this.Controls.Add(lb);



    }

    void lb_SelectedIndexChanged(object sender, EventArgs e)
    {
        Table1.Visible = false;
        Table2.Visible = false;
        getdetails(managerid);
        string comand = ((ListBox)sender).SelectedValue.ToString();
        if (comand == "create new")
        {
            Table1.Visible = true;
        }
        else
        {
            Table2.Visible = true;

            string[] emp = comand.Split('-');
            getdetails(Convert.ToInt32(emp[0]));


        }