how to bind data in DropDownList

<asp:DropDownList ID="DropDownList1" runat="server">
        </asp:DropDownList>

 SqlConnection objcon = new SqlConnection(".......");
        objcon.Open();
        SqlCommand objcmd = new SqlCommand("select * from TableName", objcon);
        SqlDataReader objreader = objcmd.ExecuteReader();
            DropDownList1.DataSource = objreader;
          //  DropDownList1.DataValueField = "Columnname";
            DropDownList1.DataTextField = "Columnname";
           DropDownList1.DataBind();