Connection String SqlConnection con =new SqlConnection(ConfigurationManager.ConnectionStrings["Con"].ConnectionString); List<string> lst = new List<string>(); private void BindListBox() { DataTable dt = new DataTable(); if (con.State != ConnectionState.Open) con.Open(); using (SqlCommand cmd = new SqlCommand(@"Select Rid,Name from Tbl_Regi", con)) { SqlDataAdapter da = new SqlDataAdapter(cmd); da.Fill(dt); //listbox1.DataSource = dt; ...