在GridView中加入CheckBox控件后,为何调试时不管我在页面怎样改变CheckBox的状态可它都不改变它的状态呢?

我的脚本是这样的:
<asp:GridView ID="GridView1" runat="server" AllowPaging="True" AutoGenerateColumns="False" CellPadding="4" ForeColor="#333333" GridLines="None" Font-Size="Small">
            <Columns>
                <asp:BoundField DataField="ID" HeaderText="产品ID" Visible="False" />
                <asp:TemplateField HeaderText="序号">
                <ItemTemplate>
                    <%# Container.DataItemIndex+1 %>
                </ItemTemplate>
                </asp:TemplateField>
                
                <asp:TemplateField HeaderText="选择">
                <ItemTemplate>
                    <asp:CheckBox ID="chkSelect" runat="server" />
                </ItemTemplate>
                </asp:TemplateField>
                <asp:BoundField DataField="ProductName" HeaderText="产品名称" />
            </Columns>
            <FooterStyle BackColor="#1C5E55" Font-Bold="True" ForeColor="White" />
            <RowStyle BackColor="#E3EAEB" HorizontalAlign="Center" />
            <EditRowStyle BackColor="#7C6F57" />
            <SelectedRowStyle BackColor="#C5BBAF" Font-Bold="True" ForeColor="#333333" />
            <PagerStyle BackColor="#666666" ForeColor="White" HorizontalAlign="Center" />
            <HeaderStyle BackColor="#1C5E55" Font-Bold="True" ForeColor="White" />
            <AlternatingRowStyle BackColor="White" />
        </asp:GridView>代码是放在一个按钮的响应事件里面:
protected void btnOK_Click(object sender, EventArgs e)
    {
        for (int i = 0; i < GridView1.Rows.Count; i++)
        {
            GridViewRow row = GridView1.Rows[i];
            bool IsCheck = ((CheckBox)row.FindControl("chkSelect")).Checked;
            if (IsCheck)
            { 
                
            }
        }
    }在程序运行时,IsCheck始终为false. 如果在脚本里面有checked属性,这里IsChecked就始终为true.即它的状态不改变.我尝试着在它的OnCheckChanged事件调用方法btnCheckBox_Click(Object sender, EventArgs e),可它在按钮按下后居然不先执行这个地方的方法.请各位帮忙看一下