GridView里绑定DropdownList

<asp:TemplateField HeaderText="是否发放" SortExpression="YesNo">
                <ItemTemplate>
                     <asp:DropDownList ID="ddl_YesNo" runat="server"  DataSource='<%# ddlbind() %>' DataTextField="YesNo"  DataValueField="YesNo">
                     </asp:DropDownList>
                 </ItemTemplate>
               <EditItemTemplate>
                     <asp:TextBox ID="TextBox30" runat="server" Text='<%# Bind("YesNo") %>'></asp:TextBox>
                </EditItemTemplate>

        //绑定数据得到这个表的所有项，
        //两个字段(1.id, 2.YesNo)       
        public DataSet ddlbind()
        {
            DataSet bbl = new BLL.J_Pay_YesNo().GetAllList();
            return bbl;
        }

        protected void gridView_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowType == DataControlRowType.DataRow)
            {
                DropDownList ddlClass = e.Row.FindControl("ddl_YesNo") as DropDownList;
                DataSet ds = bll.GetAllList();
                ddlClass.DataSource = ds;
                ddlClass.SelectedValue = DataBinder.Eval(e.Row.DataItem, "YesNo").ToString();
            }
        }