GridView中CheckBox 全選 撤選 的應用

<script type="text/javascript" language="javascript">
     function SelectChecked()
        {
            var obj = document.getElementById("gvOrderQuery_ctl01_cbxh");
            var objs = document.getElementById("gvOrderQuery").getElementsByTagName("tr");
            if(obj.checked == true)
            {
                for(var i=0;i<objs.length-1;i++)
                {
                    var objt;
                    var k = i+2;
                    if(k<10)
                        objt = document.getElementById("gvOrderQuery_ctl0"+k+"_cbx");
                    else
                        objt = document.getElementById("gvOrderQuery_ctl"+k+"_cbx");
                    objt.checked = true;
                }
            }
            else
            {
                for(var i=0;i<objs.length-1;i++)
                {
                    var objt;
                    var k = i+2;
                    if(k<10)
                        objt = document.getElementById("gvOrderQuery_ctl0"+k+"_cbx");
                    else
                        objt = document.getElementById("gvOrderQuery_ctl"+k+"_cbx");
                    objt.checked = false;
                }
            }
        }
    </script>

 <asp:GridView ID="gvOrderQuery" runat="server" Width="500px" cssClass="result_grid" EmptyDataText="沒有數據!" DataKeyNames="OrderID" AutoGenerateColumns="False" CellPadding="4"  GridLines="None">
            <Columns>
              <asp:TemplateField HeaderText = "序號">
                <ItemTemplate>
                    <asp:Label ID="Label1" runat="server" Text='<%# Container.DataItemIndex+1 %>'>
                    </asp:Label>
                  </ItemTemplate>
                  <HeaderStyle Width="40px" />
             </asp:TemplateField>
           
             <asp:BoundField DataField="OrderOutTime" HeaderText="離廠時間" DataFormatString="{0:yyyy-MM-dd HH:mm:ss}" HtmlEncode="False" />
             <asp:BoundField DataField="OrderNO" HeaderText="訂單號" />
             <asp:TemplateField>
                    <HeaderTemplate>
                       <asp:CheckBox ID="cbxh" runat="server" Text="全選" onclick = "SelectChecked()"></asp:CheckBox>
                    </HeaderTemplate>
                    <ItemTemplate>
                       <asp:CheckBox ID="cbx" runat="server" name = "cbxss" Text="選擇"></asp:CheckBox>
                    </ItemTemplate>
              </asp:TemplateField>
            </Columns>
        </asp:GridView>