binding dropdownlist in 3-tier [Resolved]

DAL 

 public class Dropdown

    {

        string _connstr = ConfigurationManager.ConnectionStrings["Connstr"].ConnectionString;

        public DataTable LoadAll()

        {

            DataTable table = new DataTable();

            using (SqlConnection con = new SqlConnection(_connstr))

            {

                string sql = "Select AutoId,FirstName from PersonDetails ORDER BY AutoId";

                using (SqlCommand cmd = new SqlCommand(sql, con))

                {

                    using (SqlDataAdapter adp = new SqlDataAdapter(cmd))

                    {

                        adp.Fill(table);

                    }

                }

            }

            return table;

        }

    }

BAL 

 public DataTable LoadAll()

        {

            DropDownList1.DAL.Dropdown drop = new Dropdown();

            return drop.LoadAll();

        }

MainWebPage(.aspx) 

//set the columname which u want to find as DataTextField and Primarykey or Autoincrement column as DataValueField for the dropdownlist

  <asp:DropDownList ID="dropdown1" runat="server" DataValueField="AutoId" DataTextField="FirstName"></asp:DropDownList>

code behind(.cs) 

  protected void Page_Load(object sender, EventArgs e)

        {

            if (!IsPostBack)

            {

                LoadAllData();

            }

           

        }

        private void LoadAllData()

        {

            DropDownList1.BAL.Class1 drop = new Class1();

            dropdown1.DataSource = drop.LoadAll();

            dropdown1.DataBind();

        }