关于DataSet绑定的有关问题

public partial class index : System.Web.UI.Page{    protected void Page_Load(object sender, EventArgs e)    {        ShowAllInfo(GetAllInfo());    }    protected void Button1_Click(object sender, EventArgs e)    {        ShowAllInfo(GetAllInfo());    }    public object GetAllInfo()    {        return QuestionBll.GetAllInfo(txtNum_case.Text.ToString(), txtNam_cust.Text.ToString(),ddl.SelectedValue.ToString(), s2.Value.ToString());    }    public void ShowAllInfo(object entities)    {        this.GridView1.DataSource = entities;        this.GridView1.DataBind();    }}

//show index        public static DataSet GetAllInfo(string num_case, string nam_cust, string sts_custcar,string dat_car)        {            string sql = "select a.typ_custcar,a.num_case,a.nam_cust,a.dat_car,a.car_note,a.solution,b.content AS nam_dept_fix,a.dat_plnfix ,a.dat_actfix,a.sts_custcar from web_caseproj_custcars a ";            sql = sql + string.Format("left join web_codd b on a.dept_fix = b.code and b.code_id = 'FIXDEPT' where 1=1 ");            if (num_case != "")            {                sql = sql + string.Format("and num_case = '{0}' ", num_case);            }            else if (nam_cust != "")            {                sql = sql + string.Format("and nam_cust = '{0}' ", nam_cust);            }            else if (sts_custcar != "")            {                sql = sql + string.Format("and sts_custcar = '{0}' ", sts_custcar);            }            else if (dat_car != "")            {                sql = sql + string.Format("and dat_car = '{0}' ", DateTime.Parse(dat_car).ToString("yyyyMMdd"));            }            else            {                sql = sql + string.Format(" order by dat_car");            }            DataSet ds = DBhelpe.ExcuteDataSet(sql);            return ds;        }