一、Aspx页面：
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="FileUploadDemo.aspx.cs" Inherits="WebApplication1.FileUploadDemo" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head id="Head1" runat="server"> <title></title> <style type="text/css"> .button{ cursor:pointer; background-color:#1481E6;border:1px solid #fff;text-align:center;height: 25px;color:#fff;line-height:19px;} </style> <script type="text/javascript"> function uploadFile(filePath) { if (filePath.length > 0) { __doPostBack(‘btnUploadFile‘, ‘‘); } } </script> </head> <body> <form id="form1" runat="server"> <div style="position: absolute; z-index: 2; cursor: pointer;"> <asp:FileUpload ID="fileUpload" runat="server" Style="filter: alpha(opacity=0); opacity: 0; cursor: pointer;" Width="70px" Height="25px" onchange="uploadFile(this.value)" accept="image/*" /> </div> <div style="position: absolute; z-index: 1; cursor: pointer; height: 25px;"> <input type="button" name="btnUploadFile" id="btnUploadFile" runat="server" value="上傳新檔案" class="button" /> </div> </form> </body> </html>
二、Aspx后台代码：
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.IO; namespace WebApplication1 { public partial class FileUploadDemo : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { btnUploadFile.ServerClick += new EventHandler(btnUploadFile_ServerClick); } void btnUploadFile_ServerClick(object sender, EventArgs e) { if (this.fileUpload.HasFile) { string fileName = this.fileUpload.PostedFile.FileName; // 客户端文件路径 string extension = System.IO.Path.GetExtension(fileName); if (extension.ToLower() != ".jpg" && extension.ToLower() != ".png") { ScriptManager.RegisterStartupScript(this, this.GetType(), "msg", "alert(‘只允许jpg 和 png！‘);", true); return; } string pathBase = "D:\\UploadFile"; if (!Directory.Exists(pathBase)) Directory.CreateDirectory(pathBase); string webFilePath = Path.Combine(pathBase, fileName); // 数据库保存文件路径（相对全路径） this.fileUpload.SaveAs(webFilePath); // 使用 SaveAs 方法保存文件 ScriptManager.RegisterStartupScript(this, this.GetType(), "msg", "alert(‘上傳成功，我們會盡快進行核對！‘);", true); } } } }
参考：http://www.cnblogs.com/Charles2008/archive/2008/07/20/1247084.html
改变FileUpload文件上传控件的显示方式，选择文件后自动上传,布布扣,bubuko.com
改变FileUpload文件上传控件的显示方式，选择文件后自动上传
原文：http://www.cnblogs.com/lusunqing/p/3832063.html