droplist用省来绑定市的操作

    public void DatabindClass2()    {        string drop1 = this.DropDownList1.SelectedValue;        DropDownList2.DataSource = new Class1_bll().SelectClasss_2(drop1);        DropDownList2.DataTextField = "cname";        DropDownList2.DataValueField = "classid_2";        DropDownList2.DataBind();    }

      #region 绑定class2表           public DataTable SelectClasss_2(string classid)          {              DataTable dt = new DataTable();              string sql = "select * from class_2 where classid_1='"+classid+"'";              dt = hepler.ExecuteQuery(sql,CommandType.Text);              return dt;          }

          #endregion