Dropdownlist select , display matching recordsto innergrid

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        using (
        SqlConnection con =
        new SqlConnection(ConfigurationManager.ConnectionStrings["testConnectionString"].ConnectionString))
        {


            using (SqlCommand cmd = new SqlCommand("usp_test_all", con))
            {
                cmd.CommandType = CommandType.StoredProcedure;
                DataTable dt = new DataTable();
                SqlDataAdapter adpt = new SqlDataAdapter(cmd);
                adpt.Fill(dt);
                DropDownList1.DataSource = dt;
                DropDownList1.DataTextField = "OrderAmount";
                DropDownList1.DataValueField = "orderID";
                DropDownList1.DataBind();
            }
        }
    }
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    using (
    SqlConnection con =
    new SqlConnection(ConfigurationManager.ConnectionStrings["testConnectionString"].ConnectionString))
    {


        using (SqlCommand cmd = new SqlCommand("usp_test", con))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@id", DropDownList1.SelectedValue);
            DataTable dt = new DataTable();
            SqlDataAdapter adpt = new SqlDataAdapter(cmd);
            adpt.Fill(dt);
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
    }
}

<div>
    <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"
        onselectedindexchanged="DropDownList1_SelectedIndexChanged">
    </asp:DropDownList>
    <asp:GridView ID="GridView1" runat="server">
    </asp:GridView>
</div>