.net利用iframe，不刷新上传文件

HTML
重点在于：

target="iframe1"
enctype="multipart/form-data"
method="post"

 1 <form id="form1" runat="server" target="iframe1" enctype="multipart/form-data" method="post">
 2         <div>
 3             <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
 4         </div>
 5         <div>
 6             <input id="File1" type="file" runat="server" />
 7             <input id="File2" type="file" runat="server" />
 8             <input id="File3" type="file" runat="server" />
 9             <input id="File4" type="file" runat="server" />
10 
11             <asp:Button ID="btn_save" runat="server" Text="上传" OnClick="btn_save_Click" Width="63px" />
12             <asp:Label ID="lbl_message" runat="server" Font-Names="方正姚体" Font-Size="9pt" ForeColor="Red"></asp:Label>
13         </div>
14     </form>
15     <iframe id="iframe1" name="iframe1" style=" 0px; height: 0px; border: none"></iframe>

后台

 1 protected void btn_save_Click(object sender, EventArgs e)
 2         {
 3             try
 4             {
 5                 //1.自带保存
 6                 for (int i = 0; i < this.Request.Files.Count; i++)
 7                 {
 8                     if (this.Request.Files[i].FileName == "")
 9                     {
10                         continue;
11                     }
12 
13                     string fileName = this.Request.Files[i].FileName.Substring(this.Request.Files[i].FileName.LastIndexOf('\') + 1);
14                 
15                     this.Request.Files[i].SaveAs(Server.MapPath("Files/" + fileName));
16                 }
17 
18                 this.Response.Write("<script>alert('保存成功')</script>");
19 
20 
21                 //2.文件流保存
22                 //string fileName = this.Request.Files[0].FileName.Substring(this.Request.Files[0].FileName.LastIndexOf('\') + 1);
23                 //System.IO.Stream fsInput = this.Request.Files[0].InputStream;
24                 //FileStream fs = File.OpenWrite(Server.MapPath("Files/" + fileName));
25                 //fsInput.CopyTo(fs, 1024);
26                 //fsInput.Flush();
27                 //fsInput.Close();
28                 //fs.Flush();
29                 //fs.Close();
30             }
31             catch (Exception ex)
32             {
33                 string a = ex.Message;
34             }
35 
36         }