.net利用iframe，不刷新上传文件

HTML
重点在于：

1. target="iframe1"
2. enctype="multipart/form-data"
3. method="post"

<form id="form1" runat="server" target="iframe1" enctype="multipart/form-data" method="post">
        <div>
            <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        </div>
        <div>
            <input id="File1" type="file" runat="server" />
            <input id="File2" type="file" runat="server" />
            <input id="File3" type="file" runat="server" />
            <input id="File4" type="file" runat="server" />

            <asp:Button ID="btn_save" runat="server" Text="上传" OnClick="btn_save_Click" Width="63px" />
            <asp:Label ID="lbl_message" runat="server" Font-Names="方正姚体" Font-Size="9pt" ForeColor="Red"></asp:Label>
        </div>
    </form>
    <iframe id="iframe1" name="iframe1" style="width: 0px; height: 0px; border: none"></iframe>

后台

protected void btn_save_Click(object sender, EventArgs e)
        {
            try
            {
                //1.自带保存
                for (int i = 0; i < this.Request.Files.Count; i++)
                {
                    if (this.Request.Files[i].FileName == "")
                    {
                        continue;
                    }

                    string fileName = this.Request.Files[i].FileName.Substring(this.Request.Files[i].FileName.LastIndexOf('\\') + 1);
                
                    this.Request.Files[i].SaveAs(Server.MapPath("Files/" + fileName));
                }

                this.Response.Write("<script>alert('保存成功')</script>");


                //2.文件流保存
                //string fileName = this.Request.Files[0].FileName.Substring(this.Request.Files[0].FileName.LastIndexOf('\\') + 1);
                //System.IO.Stream fsInput = this.Request.Files[0].InputStream;
                //FileStream fs = File.OpenWrite(Server.MapPath("Files/" + fileName));
                //fsInput.CopyTo(fs, 1024);
                //fsInput.Flush();
                //fsInput.Close();
                //fs.Flush();
                //fs.Close();
            }
            catch (Exception ex)
            {
                string a = ex.Message;
            }

        }