GridView排序加上下箭头

ASPX:

          <table width="778" border="0" align="center" cellpadding="0" cellspacing="0">
            <tr>
               <td align="center">
                    <asp:GridView  ID="myGridView" runat="server" AllowPaging="True" DataKeyNames="id"
                        AutoGenerateColumns="False" Width="100%" PageSize="25" OnRowDataBound="myGridView_RowDataBound" AllowSorting="True" OnSorting="myGridView_Sorting" OnPageIndexChanging="myGridView_PageIndexChanging" EmptyDataText="沒有記錄" OnRowCreated="myGridView_RowCreated">
                        <Columns>
                            <asp:BoundField HeaderText="序號" />
                            <asp:BoundField DataField="empno" SortExpression="empno" HeaderText="工號" />
                            <asp:BoundField DataField="cname" SortExpression="cname" HeaderText="姓名" />
                            <asp:BoundField DataField="sex" SortExpression="sex" HeaderText="性別" />
                            <asp:BoundField DataField="age" SortExpression="age" HeaderText="年齡" />
                            <asp:BoundField DataField="linecode" SortExpression="linecode" HeaderText="拉名"  />
                            <asp:BoundField DataField="hold_date" DataFormatString="{0:MM月dd日yyyy年}"  HeaderText="入廠日期"  HtmlEncode="False" SortExpression="hold_date"/>
                            <asp:BoundField DataField="g_time" DataFormatString="{0:MM月dd日yyyy年}"  HeaderText="體檢日期"  HtmlEncode="False" SortExpression="g_time"/>
                            <asp:CommandField HeaderText="操作" ShowEditButton="True" />
                            <asp:TemplateField>
                                <HeaderTemplate>
                                    <input id="CheckAll" type="checkbox" onclick="selectAll(this)" />
                                </HeaderTemplate>
                                <ItemTemplate>
                                    <input id="chkID" name="chkID" type="checkbox" value='<%# Eval("empno")%>' onclick="selectOne(this)" />
                                </ItemTemplate>
                            </asp:TemplateField>
                        </Columns>
                        <HeaderStyle BackColor="Gainsboro" />
                        <PagerSettings PageButtonCount="15" Visible="False" />
                    </asp:GridView >
              </td>
            </tr>
        </table>
       <table width="778" height="25" border="0" align="center" cellpadding="0" cellspacing="0">
        <tr>
          <td>
            <asp:Label ID="labRecordCount" runat="server"></asp:Label>&nbsp;
            <asp:Label ID="labPageCount" runat="server"></asp:Label>&nbsp;
            <asp:Label ID="labPageRecord" runat="server"></asp:Label>&nbsp;
            </td>
          <td align="right">
          <asp:LinkButton ID="btnFirst" CommandArgument="first" OnClick="PagerButtonClick" runat="server">首 页</asp:LinkButton>&nbsp;
            <asp:LinkButton ID="btnPrev" CommandArgument="prev" OnClick="PagerButtonClick" runat="server">上一页</asp:LinkButton>&nbsp;
            <asp:LinkButton ID="btnNext" CommandArgument="next" OnClick="PagerButtonClick" runat="server">下一页</asp:LinkButton>&nbsp;
          <asp:LinkButton ID="btnLast" CommandArgument="last" OnClick="PagerButtonClick" runat="server">尾 页</asp:LinkButton>
          </td>
        </tr>
      </table>

CS:

有点郁闷,在DataGrid中,页面加载的时候默认排序字段会有箭头.
GridView同样的原理就没有.只有点击的时候才有,这样的话在页面加载时就不知道按照什么排序.