绑定数据源

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
namespace lession4
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                this.BindClass();
                this.BindMaster();
            }
        }

        protected void BindClass()
        {
            SqlConnection con = new SqlConnection();
            con.ConnectionString = "server=.;database=lession;uid=sa;pwd=sa";
            con.Open();

            SqlDataAdapter sdr = new SqlDataAdapter("select * from bs_class", con);
            DataSet ds = new DataSet();
            sdr.Fill(ds);

            this.ddl_class.DataTextField = "classname";
            this.ddl_class.DataValueField = "classid";
            this.ddl_class.DataSource = ds;
            this.ddl_class.DataBind();
        }

        protected void BindMaster()
        {
            SqlConnection con = new SqlConnection();
            con.ConnectionString = "server=.;database=lession;uid=sa;pwd=sa";
            con.Open();

            SqlDataAdapter sdr = new SqlDataAdapter("select * from bs_master", con);
            DataSet ds = new DataSet();
            sdr.Fill(ds);

            this.ddl_master.DataTextField = "mastername";
            this.ddl_master.DataValueField = "masterid";
            this.ddl_master.DataSource = ds;
            this.ddl_master.DataBind();
        }
        protected void btn_add_Click(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection();
            con.ConnectionString = "server=.;database=lession;uid=sa;pwd=sa";
            con.Open();
            string sql = "insert into op_student values('"+this.txt_userno.Text+"','"+this.txt_username.Text+"',"+this.ddl_class.SelectedValue.ToString()+","+this.ddl_master.SelectedValue.ToString()+")";
            SqlCommand cmd = new SqlCommand(sql,con);
            int num = cmd.ExecuteNonQuery();
            if (num > 0)
            {
                Response.Write("<script>alert('添加成功!')</script>");
            }
            else
            {
                Response.Write("<script>alert('添加失败!')</script>");
            }
            con.Close();
        }
}
}