asp.net上传下载

<form id="form1" runat="server">
    <div>
        <asp:FileUpload ID="FileUpload1" runat="server" />&nbsp;<asp:Button ID="Button1"
            runat="server" OnClick="Button1_Click" Text="上传文件" /><br />
        <br />
        <asp:Image ID="Image1" runat="server" Height="300px" Width="300px" /><br />
        <br />
        <br />
        <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" Height="200px"
            Width="500px">
            <Columns>
                <asp:HyperLinkField DataNavigateUrlFields="FileName" DataNavigateUrlFormatString="UpDownFile.aspx?id={0}"
                    DataTextField="FileName" HeaderText="FileName" />
                <asp:BoundField DataField="CreateTime" HeaderText="CreateTime" />
            </Columns>
        </asp:GridView>
    
    </div>
</form>

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.IO;

public partial class Up__Down_File : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Bind();
        }
        if (Request.QueryString["id"] != null) //接收用户要下载的文件ID
        {
            string file = Request.QueryString["id"];
            Response.AddHeader("content-disposition", "attachment;filename=" + Server.UrlEncode(file));
            Response.WriteFile(Server.MapPath("~/UpLoad/") + file);
            Response.Flush();
            Response.End();
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        if (FileUpload1.FileName != null) //上传文件显示在图片框
        {
            FileUpload1.SaveAs(Server.MapPath("~/UpLoad/")+ FileUpload1.FileName);
            Image1.ImageUrl = "~/UpLoad/" + FileUpload1.FileName;
            Image1.Visible = true;
        }
    }
    void Bind()  //绑定读取下载文件夹文件信息到GridView
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("FileName", typeof(string));
        dt.Columns.Add("CreateTime", typeof(DateTime));
        foreach (string file in Directory.GetFiles(Server.MapPath("~/UpLoad/")))
        {
            DataRow dr = dt.NewRow();
            dr[0] = Path.GetFileName(file);
            dr[1] = File.GetCreationTime(file);
            dt.Rows.Add(dr);
        }
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}