看看效果：
在专案中，创建aspx页面，拉上FileUpload控件一个Image，将用来预览上传时的图片。
View Code
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<table>
<tr>
<td style="vertical-align: top; 10%;">
<fieldset>
<legend>选择图片</legend>
<asp:FileUpload ID="FileUpload1" runat="server" />
</fieldset>
</td>
<td style="vertical-align: top; 90%;">
<fieldset>
<legend>预览</legend>
<asp:Image ID="Image1" runat="server" Visible="false" />
</fieldset>
</td>
</tr>
</table>
</div>
</form>
</body>
</html>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<table>
<tr>
<td style="vertical-align: top; 10%;">
<fieldset>
<legend>选择图片</legend>
<asp:FileUpload ID="FileUpload1" runat="server" />
</fieldset>
</td>
<td style="vertical-align: top; 90%;">
<fieldset>
<legend>预览</legend>
<asp:Image ID="Image1" runat="server" Visible="false" />
</fieldset>
</td>
</tr>
</table>
</div>
</form>
</body>
</html>
在Page_Init事件中，为FileUpload控件，注册onchange客户端事件。
View Code
protected void Page_Init(object sender, EventArgs e)
{
this.FileUpload1.Attributes.Add("onchange", Page.ClientScript.GetPostBackEventReference(this.FileUpload1, "onchange"));
}
{
this.FileUpload1.Attributes.Add("onchange", Page.ClientScript.GetPostBackEventReference(this.FileUpload1, "onchange"));
}
接下来，Insus.NET创建一个axd处理文档，其实ImageProcessFactory.cs只是一个普通的类别，只实作了IHttpHandler接口。
ImageProcessFactory.cs
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Web;
using System.Web.SessionState;
/// <summary>
/// Summary description for ImageProcessFactory
/// </summary>
namespace Insus.NET
{
public class ImageProcessFactory : IHttpHandler,IRequiresSessionState
{
public ImageProcessFactory()
{
//
// TODO: Add constructor logic here
//
}
public void ProcessRequest(HttpContext context)
{
//Checking whether the UploadBytes session variable have anything else not doing anything
if ((context.Session["UploadBytes"]) != null)
{
byte[] buffer = (byte[])(context.Session["UploadBytes"]);
context.Response.BinaryWrite(buffer);
}
}
public bool IsReusable
{
get
{
return false;
}
}
}
}
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Web;
using System.Web.SessionState;
/// <summary>
/// Summary description for ImageProcessFactory
/// </summary>
namespace Insus.NET
{
public class ImageProcessFactory : IHttpHandler,IRequiresSessionState
{
public ImageProcessFactory()
{
//
// TODO: Add constructor logic here
//
}
public void ProcessRequest(HttpContext context)
{
//Checking whether the UploadBytes session variable have anything else not doing anything
if ((context.Session["UploadBytes"]) != null)
{
byte[] buffer = (byte[])(context.Session["UploadBytes"]);
context.Response.BinaryWrite(buffer);
}
}
public bool IsReusable
{
get
{
return false;
}
}
}
}
为能应用到axd文档，需要在Web.Config中配置一下。
View Code
<configuration>
<system.web>
<httpHandlers>
<add verb="*" path="PreviewImage.axd" type="Insus.NET.ImageProcessFactory"/>
</httpHandlers>
</system.web>
</configuration>
<system.web>
<httpHandlers>
<add verb="*" path="PreviewImage.axd" type="Insus.NET.ImageProcessFactory"/>
</httpHandlers>
</system.web>
</configuration>
Ok，我们回到aspx.cs页面中，要在page_Load中，怎监控FileUpload控件是否有值变化：
View Code
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
var ctrl = Request.Params[Page.postEventSourceID];
var args = Request.Params[Page.postEventArgumentID];
OnchangeHandle(ctrl, args);
}
}
{
if (IsPostBack)
{
var ctrl = Request.Params[Page.postEventSourceID];
var args = Request.Params[Page.postEventArgumentID];
OnchangeHandle(ctrl, args);
}
}
在Page_Load中有一个方法OnchangeHandle(xxx,xxx):
View Code
private void OnchangeHandle(string ctrl, string args)
{
if (ctrl == this.FileUpload1.UniqueID && args == "onchange")
{
this.Image1.Visible = true;
Session["UploadBytes"] = this.FileUpload1.FileBytes;
this.Image1.ImageUrl = "~/PreviewImage.axd" ;
}
}
{
if (ctrl == this.FileUpload1.UniqueID && args == "onchange")
{
this.Image1.Visible = true;
Session["UploadBytes"] = this.FileUpload1.FileBytes;
this.Image1.ImageUrl = "~/PreviewImage.axd" ;
}
}
以下内容于2016-02-16 13:56分添加：
一段时间以来，得到许多网友关注这个功能，但网友在测试时，均不能成功执行。
有几点需要注意的，ImageProcessFactory.cs只是一个普通的类别。而不是一般处理程序。另外在较高的.net版下测试时，它会出现下面异常：
它会出现一个异常：
解决这个问题，你可以尝试下面的步骤来进行：
把Integrated改为Classic：
当你完成上面的修改之后，网站程序文件下会生成一个xml格式的文件vwd.webinfo：
另外Insus.NET再附加最新的写的源程序，可从下面链接下载：
http://download.cnblogs.com/insus/ASPDOTNET/AxdDemo.rar