GridView加入CheckBox实现当前页全选或反选

<script type="text/javascript" language="javascript">
    //反选
    function backSelectAll(obj)
    {
        var theTable  = obj.parentElement.parentElement.parentElement; 
        var j = obj.parentElement.cellIndex;
        for(var i=0;i<theTable.rows.length;i++)
        {
            var objCheckBox = theTable.rows[i].cells[j].firstChild;
            if(objCheckBox.checked == false)
            {
                objCheckBox.checked = true;
            }
            else
            {
                objCheckBox.checked = false;
            }
        }
    }
    //全选
    function selectAll(obj)
    {
        var theTable  = obj.parentElement.parentElement.parentElement;
        var j = obj.parentElement.cellIndex;  
        for(var i=0;i<theTable.rows.length;i++)
        {
            var objCheckBox = theTable.rows[i].cells[j].firstChild;
            if(objCheckBox.checked!=null)objCheckBox.checked = obj.checked;
        }
    }
</script>

<asp:templatefield>
    <headertemplate>
        <a onclick="backSelectAll(this);" href="#">反选</a><!--反选-->
        <input id="CheckAll" type="checkbox" onclick="selectAll(this);" /><!--全选-->
    </headertemplate>
    <itemtemplate>
        <asp:checkbox id="CheckBox1" runat="server" /><!--单选-->
    </itemtemplate>
</asp:templatefield>