DataGrid的模板列如何绑定DropDownList

帮看下，有问题吗，一打开dropDownList的选项就是空白的，而同行的，其它列已正确显示数据。

<asp:TemplateColumn HeaderStyle-HorizontalAlign="Center" HeaderText="交费方式">
<HeaderStyle HorizontalAlign="Center"></HeaderStyle>
<ItemTemplate>
<asp:DropDownList ID="manner" Width="80" DataTextField="mannerName" DataValueField="mannerID" Runat="server"></asp:DropDownList>
</ItemTemplate>
</asp:TemplateColumn>

private void dgMain_ItemDataBound(object sender, System.Web.UI.WebControls.DataGridItemEventArgs e )
{
if(e.Item.ItemType==ListItemType.Item||e.Item.ItemType==ListItemType.AlternatingItem)
{
DropDownList mannerDLst=(DropDownList)dgMain.Items[6].FindControl("manner");
string SQLmanner;
SqlConnection htrlConn=classes.Base.getConn(Session["year"].ToString());
SQLmanner="select mannerID,mannerName from TB_Manner where mannerID in(3,4,6)";
SqlDataAdapter mannerCommand=new SqlDataAdapter(SQLmanner,htrlConn);
DataSet DS=new DataSet();
mannerCommand.Fill(DS);
mannerDLst.DataSource=DS.Tables[0].DefaultView;
mannerDLst.DataTextField="mannerName";
mannerDLst.DataValueField="mannerID";
mannerDLst.DataBind();
htrlConn.Close();
}

}