DropdownList异步刷新GridView数据

前台代码：

    <div style=" clear:both; 800px; text-align:center; margin-left:auto; margin-right:auto; margin-left:270px">
    <table>
        <tr>
            <td style="font-weight: bold; font-size: 20px; text-align: center" 
                class="style556">
                <asp:Label ID="lblTitle" runat="server"></asp:Label>
            </td>
        </tr>
        <tr>
            <td align="right">
              时间：<asp:DropDownList ID="ddlDate" runat="server" AutoPostBack="True" OnSelectedIndexChanged="ddlDate_SelectedIndexChanged">
                    </asp:DropDownList>
                     
            </td>
        </tr>
        <tr>
            <td style="text-align:right">
                <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                    <ContentTemplate>
                   
                <yyc:SmartGridView ID="sgvFile" runat="server" AllowPaging="True" AutoGenerateColumns="False"
                    DataKeyNames="Id" OnPageIndexChanging="SmartGridView_PageIndexChanging" PageSize="30"
                    SkinID="UnpagedWrap" Width="790px" MergeCells="5,6,7,8">
                    <Columns>
                        <asp:BoundField DataField="Id" HeaderText="Id" Visible="False" />
                        <asp:TemplateField HeaderText="方向">
                            <ItemTemplate>
                                <asp:Label ID="lbyinyong" runat="server" Text='<%# Eval("LeftOrRight").ToString()=="1"?"进洞口":"出洞口" %>'></asp:Label>
                            </ItemTemplate>
                            <ItemStyle Width="70px" />
                        </asp:TemplateField>
                        <asp:BoundField DataField="ClassName" HeaderText="工序名称" />
                        <asp:BoundField DataField="AllLength" DataFormatString="{0:0.##}" HeaderText="长度<br/>"
                            HtmlEncode="False" />
                        <asp:TemplateField HeaderText="截止上日末<br/>数量(m)">
                            <ItemTemplate>
                                <%# Convert.ToInt32(Eval("LeftOrRight")) == 1 ? Eval("AllFinishL") : Eval("AllFinishR")%>
                            </ItemTemplate>
                        </asp:TemplateField>
                        <asp:BoundField DataField="FinishNumber" DataFormatString="{0:0.##}" HeaderText="本日数量<br/>(m)"
                            HtmlEncode="False" />
                        <asp:BoundField DataField="AllFinish" DataFormatString="{0:0.##}" HeaderText="累计完成<br/>数量(m)"
                            HtmlEncode="False" />
                        <asp:BoundField DataField="PercentFinish" DataFormatString="{0:0.##}%" HeaderText="累计完成<br/>百分比"
                            HtmlEncode="False" />
                        <asp:BoundField DataField="NoFinishNumber" DataFormatString="{0:0.##}" HeaderText="剩余量<br/>(m)"
                            HtmlEncode="False" />
                        <asp:BoundField DataField="AddDate" DataFormatString="{0:d}" HeaderText="日期" HtmlEncode="False"
                            ReadOnly="True">
                            <ItemStyle HorizontalAlign="Center" />
                        </asp:BoundField>
                        <asp:TemplateField HeaderText="监理<br>审核">
                            <ItemTemplate>
                                <asp:Label ID="Label1" Text='<%# zhy_CommClass.zhyPageView.IsPassView(Eval("Pass"), "已审", "<font color=red>未审</font>")                                         %>' runat="server"></asp:Label> 
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
                </yyc:SmartGridView>

                 </ContentTemplate>
                 <Triggers>
                 　　<asp:AsyncPostBackTrigger ControlID="ddlDate" />
                 </Triggers>
                </asp:UpdatePanel>
            </td>
        </tr>
    </table>
    </div>