GridView CheckBox validation using JavaScript jQuery and ASP.Net CustomValidator

This way

    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script type = "text/javascript">
        function ValidateCheckBoxes(sender, args) {
            args.IsValid = $("[id$=GridView1] input:checked").length > 1;
        }
    </script>
    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:CheckBox ID="CheckBox1" runat="server" />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:BoundField DataField="Item" />
            <asp:BoundField DataField="Code" />
        </Columns>
    </asp:GridView>
    <asp:Button ID="Button1" runat="server" Text="Button" />
    <asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="Please check atleast one checkbox" ClientValidationFunction = "ValidateCheckBoxes"></asp:CustomValidator>

    protected void Page_Load(object sender, EventArgs e)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[2] { new DataColumn("Item"), new DataColumn("Code") });
        dt.Rows.Add("Shirt", 199);
        dt.Rows.Add("Football", 020);
        dt.Rows.Add("Shirt", 566);
        dt.Rows.Add("Disc", 099);
        dt.Rows.Add("Watch", 54);
        dt.Rows.Add("Clock", 890);
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }