NET GridView中添加CheckBox取值问题

前台代码：

<asp:GridView ID="GridviewDeptAuditList" AutoGenerateColumns="false" runat="server"
            GridLines="none" Width="100%"
            <AlternatingRowStyle CssClass="alt" />
            <Columns>
                <asp:TemplateField ItemStyle-Width="6%">
                    <HeaderTemplate>
                        <asp:CheckBox ID="selectAll" runat="server" onclick="getAllCheckBox(this)" />
                        <span>全选</span>
                    </HeaderTemplate>
                    <ItemTemplate>
                        <asp:CheckBox ID="itemSelect" runat="server" />
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField ItemStyle-Width="5%">
                    <HeaderTemplate>
                        查看</HeaderTemplate>
                    <ItemTemplate>
                        <a href='<%#GetAllUrl(Eval("ID")) %>'>查看</a>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:BoundField HeaderText="流程名称" DataField="WorkFlowName" ItemStyle-Width="14%" />
                <asp:BoundField HeaderText="子流程名称" DataField="SubWorkflowName" ItemStyle-Width="14%" />
            </Columns>
        </asp:GridView>

js实现全选效果：

 <script type="text/javascript">
        function getAllCheckBox(checkAll) {
            var items = document.getElementsByTagName("input");
            for (i = 0; i < items.length; i++) {
                if (items[i].type == "checkbox") {
                    items[i].checked = checkAll.checked;
                }
            }
        }
</script>

后台代码：

//注意：如果是在page_load里绑定GridView,一定要加上(!Page.IsPostBack），不然取不到值的。我就是在这上面吃了亏。

   protected void Page_Load(object sender, EventArgs e)
        {
            this.EnableProgressBar = false;
            if (!Page.IsPostBack)
            {
                BindGridView();
            }
        }
        public void BindGridView()
        {
            this.Gridview1.DataSource = dataSource;
            this.Gridview1.DataKeyNames = new string[] { "ID" };
            this.Gridview1t.DataBind();
        }

取值方法：

  protected void BtnDeny_Click(object sender, EventArgs e)
        {
            // 取值 
            for (int i = 0; i < GridviewDeptAuditList.Rows.Count; i++)
            {
                CheckBox chb = (CheckBox)Gridview1.Rows[i].FindControl("itemSelect");
                if (chb.Checked)
                {

                    keys += GridviewDeptAuditList.DataKeys[i].Value.ToString() + ",";
                }

            }
        }