asp.net gridview多页时的批量删除

<asp:GridView ID="grwBook" runat="server" CellPadding="4" ForeColor="#333333" GridLines="None" AutoGenerateColumns="false" AllowPaging="true" DataKeyNames="ID" OnPageIndexChanging="grwBook_PageIndexChanging" PageSize="12">
    <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
    <RowStyle BackColor="#EFF3FB" />
    <EditRowStyle BackColor="#2461BF" />
    <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
    <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
    <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
    <AlternatingRowStyle BackColor="White" />
    <Columns>
    <asp:BoundField DataField="ID" HeaderText = "ID" />
    <asp:BoundField DataField="UserName" HeaderText="姓名">
    <ItemStyle Width="60px" />
    </asp:BoundField>
    <asp:BoundField DataField="Comments" HeaderText="评论">
    <ItemStyle width="500px"  />
    </asp:BoundField>
    <asp:BoundField DataField="Postdate" HeaderText="日期" />
    <asp:HyperLinkField DataNavigateUrlFields="newsid" DataNavigateUrlFormatString="../news_zi.asp?id={0}" HeaderText="文章"  DataTextField="newsid" target="_blank" />
    <asp:TemplateField HeaderText="操作" >
        <ItemTemplate>
        <asp:CheckBox runat="Server" ID="cbxId" />
        </ItemTemplate>
    </asp:TemplateField>
    </Columns>
    <PagerSettings Mode="NextPreviousFirstLast" FirstPageText="第一页" LastPageText="末页" NextPageText="下一页" PreviousPageText="上一页" />
</asp:GridView>

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.OleDb;

public partial class admin_book_admin : System.Web.UI.Page
{

    
    protected void Page_Load(object sender, EventArgs e)
    {
        //判断管理员是否已经登陆
        admin.checkadmin();

        btnDel.Attributes.Add("onclick", "return confirm('确定删除吗？')");

        if (!Page.IsPostBack)
        {
            datainit();
        }
    }

    protected void grwBook_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
        this.grwBook.PageIndex = e.NewPageIndex;
        Session["curretnPage"] = e.NewPageIndex;
        datainit();
    }

    //数据绑定
    private void datainit()
    {
        DataSet ds = db.dataSet("select ID,UserName,Comments,Postdate,newsid from Feedback order by Postdate desc,newsid desc");
        if (ViewState["currentPage"] != null)
        {
            this.grwBook.PageIndex = Convert.ToInt32(Session["currentPage"]);
        }
        this.grwBook.DataSource = ds;
        this.grwBook.DataBind();

    }

    //执行删除操作
    protected void btnDel_Click(object sender, EventArgs e)
    {
        string sqlText = "(";
        for (int i = 0; i < grwBook.Rows.Count; i++)
        {
            //搜索第n行3列
            CheckBox cbx = (CheckBox)grwBook.Rows[i].FindControl("cbxId");
            if (cbx.Checked == true)
            {
               sqlText = sqlText + Convert.ToInt32(grwBook.DataKeys[i].Value) + ",";
            }
        }

        //判断是否有选中
        if (sqlText != "(")
        {
            //去掉最后的逗号，并且加上右括号
            sqlText = sqlText.Substring(0, sqlText.Length - 1) + ")";
            sqlText = "delete from Feedback where ID in" + sqlText;
            try
            {
                //执行删除语句
                db.excuteSql(sqlText);
                //重新绑定数据
                common.salert("删除成功");
                datainit();
                //Response.Redirect("book_admin.aspx");
            }
            catch (Exception ex)
            {
                //若有错误发生，输出错误信息
                common.salert(ex.Message);
            }
            finally
            {

            }
        }
        else
        {
            common.salert("您还没有选中有删除的项");
        }
    }


}