js gridview中checkbox的全选与全不选

1.html：

  <asp:GridView runat="server" ID="gvAddBySR" AutoGenerateColumns="False" HorizontalAlign="Left"
            Width="100%" EmptyDataText="<%$ Resources:GlobalResource,  NoData%>">
            <Columns>
                <asp:TemplateField HeaderStyle-Width="7%">
                    <HeaderTemplate>
                        <input id="CheckAll" type="checkbox" onclick="selectAll(this);" />
                    </HeaderTemplate>
                    <ItemTemplate>
                        <asp:CheckBox runat="server" ID="ck" class="ck" onclick="getCk(this);"/>
                    </ItemTemplate>
                </asp:TemplateField>

2.js

 function selectAll(obj) {
         var idAll = obj;
         Ced = idAll.checked;
         UCed = idAll.form.elements;
         var c = UCed.length;
         for (i = 0; i < UCed.length; i++) {
             if (UCed[i].type == "checkbox" && UCed[i] != idAll.id) {
                 if (UCed[i].checked != Ced) {
                     UCed[i].click();
                 }
             }
         }
     }