private void loadThanhPho()
 {
     ddlThanhPho.DataSource     = tp.LoadDuLieu();
     ddlThanhPho.DataValueField = "ID_ThanhPho";
     ddlThanhPho.DataTextField  = "TenThanhPho";
     ddlThanhPho.DataBind();
 }
 protected void Page_Load(object sender, EventArgs e)
 {
     if (!Page.IsPostBack)
     {
         ddlThanhPho.DataSource     = tp.LoadDuLieu();
         ddlThanhPho.DataTextField  = "TenThanhPho";
         ddlThanhPho.DataValueField = "ID_ThanhPho";
         ddlThanhPho.DataBind();
     }
 }