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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(‘上传成功！‘);", true);
}
}
}
}
改变FileUpload文件上传控件的显示方式，选择文件后自动上传
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原文地址：http://www.cnblogs.com/wdx-621/p/5177701.html
