绑定省里的市

Question

        if (!this.IsPostBack)
        {
            //绑定省
            SqlConnection con = DB.creatConnection();
            con.Open();
            SqlCommand cmd = new SqlCommand("select *from province", con);
            SqlDataReader sdr = cmd.ExecuteReader();
            this.ddlprovince.DataSource = sdr;
            this.ddlprovince.DataTextField = "proname";
            this.ddlprovince.DataBind();
            sdr.Close();
           // 绑定市            SqlCommand cmdcity = new SqlCommand("select *from city where proid="+this.ddlprovince.SelectedValue, con);
            sdr = cmdcity.ExecuteReader();
            this.ddlcity.DataSource = sdr;
            this.ddlcity.DataTextField = "cityname";
            this.ddlcity.DataValueField = "cityid";
            this.ddlcity.DataBind();
            sdr.Close();
            con.Close();
        }
        有什么问题啊，他显示的是“北京'无效

Answer 1

if (!this.IsPostBack)
  {
  //绑定省
  SqlConnection con = DB.creatConnection();
  con.Open();
  SqlCommand cmd = new SqlCommand("select *from province", con);
  SqlDataReader sdr = cmd.ExecuteReader();
  this.ddlprovince.DataSource = sdr;
  this.ddlprovince.DataTextField = "proname";
  this.ddlprovince.DataValueField = "proid";//加上这行 省一定有id 字段名称你自己对应
  this.ddlprovince.DataBind();
  sdr.Close();
  // 绑定市  SqlCommand cmdcity = new SqlCommand("select * from city where proid="+this.ddlprovince.SelectedValue, con);
  sdr = cmdcity.ExecuteReader();
  this.ddlcity.DataSource = sdr;
  this.ddlcity.DataTextField = "cityname";
  this.ddlcity.DataValueField = "cityid";
  this.ddlcity.DataBind();
  sdr.Close();
  con.Close();
  }