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