asp.net中数据绑定

private void Page_Load(object sender, System.EventArgs e)
{
// 在此处放置用户代码以初始化页面
if(!Page.IsPostBack)
{
//绑定省
SqlConnection con = DB.createConnection();
con.Open();
SqlCommand cmd = new SqlCommand("select * from prcvince",con);
SqlDataReader sdr = cmd.ExecuteReader();
this.ddlprcvince.DataSource = sdr;
this.ddlprcvince.DataTextField = "proName";
this.ddlprcvince.DataValueField ="proID";
this.ddlprcvince.DataBind();
sdr.Close();

//绑定市
SqlCommand cmdcity = new SqlCommand("select * from City where proID="+this.ddlprcvince.SelectedValue,con);
sdr = cmdcity.ExecuteReader();
this.ddlCity.DataSource = sdr;
this.ddlCity.DataTextField = "cityName";
this.ddlCity.DataValueField ="cityID";
this.ddlCity.DataBind();
sdr.Close();
//关闭数据