省市联动 DropDownList AutoPostBack

protected void Page_Load(object sender, EventArgs e)
    {
        SQLHelper sqH;
        if (!Page.IsPostBack)
        {
            sqH = new SQLHelper();
            string strSelPro = "SELECT [proName] FROM [db_city].[dbo].[tb_province] ";
            DataTable dt = sqH.ExecuteQuery(strSelPro,CommandType.Text);
            if (dt.Rows.Count > 0)
            {
                DropDownList1.DataSource = dt;
                DropDownList1.DataValueField = dt.Columns[0].ColumnName;
                DropDownList1.DataTextField = dt.Columns[0].ColumnName;
                DropDownList1.DataBind();
            }


            //try
            //{
            //    using (SqlConnection sqlCon = new SqlConnection("server=.;database=db_city;uid=sa;pwd="))
            //    {
            //        sqlCon.Open();
            //        string strSelPro = "SELECT [proName] FROM [db_city].[dbo].[tb_province] ";
            //        SqlCommand sqlCom = new SqlCommand(strSelPro, sqlCon);
            //        SqlDataReader sdr = sqlCom.ExecuteReader();
            //        while (sdr.Read())
            //        {
            //            DropDownList1.Items.Add(sdr[0].ToString());
            //        }
            //        sdr.Close();

            //        string strSelCity = "SELECT [proName],b.[cityName],a.[proID],b.[proID] FROM [db_city].[dbo].[tb_province] as a,[db_city].[dbo].[tb_city] as b  ";
            //        strSelCity += "where a.[proID]=b.[proID] and [proName]='" + DropDownList1.SelectedItem.Text + "'";
            //        sqlCom = new SqlCommand(strSelCity, sqlCon);
            //        sdr = sqlCom.ExecuteReader();
            //        while (sdr.Read())
            //        {
            //            DropDownList2.Items.Add(sdr[1].ToString());
            //        }
            //        sdr.Close();
            //    }
            //}
            //catch (Exception ex)
            //{
            //    throw ex;
            //}
            //finally
            //{
            //}
            
        }
        
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        //DropDownList2.Items.Clear();
        //try
        //{
        //    using (SqlConnection sqlCon = new SqlConnection("server=.;database=db_city;uid=sa;pwd="))
        //    {
        //        sqlCon.Open();
        //        string strSelCity = "SELECT [proName],b.[cityName],a.[proID],b.[proID] FROM [db_city].[dbo].[tb_province] as a,[db_city].[dbo].[tb_city] as b  ";
        //        strSelCity += "where a.[proID]=b.[proID] and [proName]='" + DropDownList1.SelectedItem.Text + "'";
        //        SqlCommand sqlCom = new SqlCommand(strSelCity, sqlCon);
        //        SqlDataReader sdr = sqlCom.ExecuteReader();
        //        while (sdr.Read())
        //        {
        //            DropDownList2.Items.Add(sdr[1].ToString());
        //        }
        //        sdr.Close();
        //    }
        //}
        //catch (Exception ex)
        //{
        //    throw ex;
        //}
        //finally
        //{
        //}
    }