asp.net中打印指定控件内容

1.写一个PrintHelper类
using System;
using System.Data;
using System.Configuration;
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.IO;
using System.Text;
using System.Web.SessionState;
namespace PrintPage
{
 
    public class PrintHelper
    {
        public PrintHelper()
        { }
        public static void PrintWebControl(Control control)
        {
            PrintWebControl(control, string.Empty);
        }
        public static void PrintWebControl(Control control, string Script)
        {
            StringWriter stringWrite = new StringWriter();
            HtmlTextWriter htmlWriter = new HtmlTextWriter(stringWrite);
            if (control is WebControl)
            {
                Unit w = new Unit(100, UnitType.Percentage);
                ((WebControl)control).Width = w;
            }
            Page pg = new Page();
            pg.EnableEventValidation = false;
            if (Script != string.Empty)
            {
                pg.ClientScript.RegisterStartupScript(pg.GetType(), "PrintJavaScipt", Script);
            }
            HtmlForm frm = new HtmlForm();
            pg.Controls.Add(frm);
            frm.Attributes.Add("runat", "server");
            frm.Controls.Add(control);
            pg.RenderControl(htmlWriter);
            string strHTML = stringWrite.ToString();
            HttpContext.Current.Response.Clear();
            HttpContext.Current.Response.Write(strHTML);
            HttpContext.Current.Response.Write("<script>window.print();</script>");
            HttpContext.Current.Response.End();
        }
    }
}

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;
namespace PrintPage
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
        }
        protected void btnPrint_Click(object sender, EventArgs e)
        {
            Session["control"] = Panel1;
            ClientScript.RegisterStartupScript(this.GetType(), "onclick", "<script language=javascript>window.open('Print.aspx','PrintMe','height=300px,width=300px,scrollbars=1');</script>");
        }
    }
}

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;
namespace PrintPage
{
    public partial class Print : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            Control control = (Control)Session["control"];
            PrintHelper.PrintWebControl(control);
        }
    }
}