出于安全性能的考虑，目前js端不支持获取本地图片进行预览，正好在做一款类似于QQ心情的发布框，找了不少jquery插件，没几个能满足需求，因此自己使用SWFuplad来实现这个图片上传预览。
先粘上以下插件，在别的图片上传功能说不定各位能用的上。
1、jQuery File Upload Demo地址：http://blueimp.github.io/jQuery-File-Upload/
优点是使用jquery进行图片的异步上传，可控性好，可根据自己的需求任意定制；
缺点是在IE9等一些浏览器中，不支持图片预览，图片选择框中不支持多文件选择（这点是我抛弃它的原因）；
2、CFUpdate Demo地址：http://www.access2008.cn/update/
优点：使用js+flash实现，兼容所有浏览器，优点界面效果还可以，支持批量上传、支持预览、进度条、删除等功能，作为图片的上传控件非常好用；
缺点：定制型插件，只能修改颜色，样式已经固定死了；
3、SWFUpload
下载地址：http://code.google.com/p/swfupload/
中文文档帮助地址：http://www.phptogether.com/swfuploadoc/#uploadError
本文所使用的就是此插件，使用flash+jquery实现，可以更改按钮及各种样式；监听事件也很全。
以下贴出源码及设计思路，主要功能点包括：
1、图片的上传预览（先将图片上传至服务器，然后再返回地址预览，目前抛开html5比较靠谱的预览方式）
2、缩略图的产生（等比例缩放后再截取中间区域作为缩略图，类似QQ空间的做法，不过貌似QQ空间加入了人脸识别的功能）
以下是此次实现的功能截图：
1、Thumbnail.cs
public class Thumbnial
{
/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="imgSource">原图片</param>
/// <param name="newWidth">缩略图宽度</param>
/// <param name="newHeight">缩略图高度</param>
/// <param name="isCut">是否裁剪（以中心点）</param>
/// <returns></returns>
public static Image GetThumbnail(System.Drawing.Image imgSource, int newWidth, int newHeight, bool isCut)
{
int rWidth = 0; // 等比例缩放后的宽度
int rHeight = 0; // 等比例缩放后的高度
int sWidth = imgSource.Width; // 原图片宽度
int sHeight = imgSource.Height; // 原图片高度
double wScale = (double)sWidth / newWidth; // 宽比例
double hScale = (double)sHeight / newHeight; // 高比例
double scale = wScale < hScale ? wScale : hScale;
rWidth = (int)Math.Floor(sWidth / scale);
rHeight = (int)Math.Floor(sHeight / scale);
Bitmap thumbnail = new Bitmap(rWidth, rHeight);
try
{
// 如果是截取原图，并且原图比例小于所要截取的矩形框，那么保留原图
if (!isCut && scale <= 1)
{
return imgSource;
}
using (Graphics tGraphic = Graphics.FromImage(thumbnail))
{
tGraphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; /* new way */
Rectangle rect = new Rectangle(0, 0, rWidth, rHeight);
Rectangle rectSrc = new Rectangle(0, 0, sWidth, sHeight);
tGraphic.DrawImage(imgSource, rect, rectSrc, GraphicsUnit.Pixel);
}
if (!isCut)
{
return thumbnail;
}
else
{
int xMove = 0; // 向右偏移（裁剪）
int yMove = 0; // 向下偏移（裁剪）
xMove = (rWidth - newWidth) / 2;
yMove = (rHeight - newHeight) / 2;
Bitmap final_image = new Bitmap(newWidth, newHeight);
using (Graphics fGraphic = Graphics.FromImage(final_image))
{
fGraphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; /* new way */
Rectangle rect1 = new Rectangle(0, 0, newWidth, newHeight);
Rectangle rectSrc1 = new Rectangle(xMove, yMove, newWidth, newHeight);
fGraphic.DrawImage(thumbnail, rect1, rectSrc1, GraphicsUnit.Pixel);
}
thumbnail.Dispose();
return final_image;
}
}
catch (Exception e)
{
return new Bitmap(newWidth, newHeight);
}
}
}
2、图片上传处理程序Upload.ashx
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Drawing;
namespace Mood
{
/// <summary>
/// Upload 的摘要说明
/// </summary>
public class Upload : IHttpHandler
{
Image thumbnail;
public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "text/plain";
try
{
string id = System.Guid.NewGuid().ToString();
HttpPostedFile jpeg_image_upload = context.Request.Files["Filedata"];
Image original_image = System.Drawing.Image.FromStream(jpeg_image_upload.InputStream);
original_image.Save(System.Web.HttpContext.Current.Server.MapPath("~/Files/" + id + ".jpg"));
int target_width = 200;
int target_height = 150;
string path = "Files/Files200/" + id + ".jpg";
string saveThumbnailPath = System.Web.HttpContext.Current.Server.MapPath("~/" + path);
thumbnail = Thumbnial.GetThumbnail(original_image, target_width, target_height, true);
thumbnail.Save(saveThumbnailPath);
context.Response.Write(path);
}
catch (Exception e)
{
// If any kind of error occurs return a 500 Internal Server error
context.Response.StatusCode = 500;
context.Response.Write("上传过程中出现错误!");
}
finally
{
if (thumbnail != null)
{
thumbnail.Dispose();
}
}
}
public bool IsReusable
{
get
{
return false;
}
}
}
}
3、前台界面Mood.aspx
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Mood.aspx.cs" Inherits="Mood.Mood" %>
<!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 runat="server">
<script src="SwfUpload/swfupload.js" type="text/javascript"></script>
<script src="jquery-1.7.1.js" type="text/javascript"></script>
<link href="Style/Mood.css" rel="stylesheet" type="text/css" />
<title></title>
<script type="text/javascript">
$().ready(function () {
SetSwf();
$("#btnReply").click(function () {
$("#divImgs").hide();
});
});
var swfu;
function SetSwf() {
swfu = new SWFUpload({
// Backend Settings
upload_url: "Upload.ashx",
// File Upload Settings
file_size_limit: "20 MB",
file_types: "*.jpg;*.png;*jpeg;*bmp",
file_types_description: "JPG;PNG;JPEG;BMP",
file_upload_limit: "0", // Zero means unlimited
file_queue_error_handler: fileQueueError,
file_dialog_complete_handler: fileDialogComplete,
upload_progress_handler: uploadProgress,
upload_error_handler: uploadError,
upload_success_handler: uploadSuccess,
upload_complete_handler: uploadComplete,
// Button settings
button_image_url: "/Style/Image/4-16.png",
button_placeholder_id: "divBtn",
button_width: 26,
button_height: 26,
// Flash Settings
flash_url: "/swfupload/swfupload.swf",
custom_settings: {
upload_target: "divFileProgressContainer"
},
// Debug Settings
debug: false
});
}
// 文件校验
function fileQueueError(file, errorCode, message) {
try {
switch (errorCode) {
case SWFUpload.QUEUE_ERROR.ZERO_BYTE_FILE:
alert("上传文件有错误！");
break;
case SWFUpload.QUEUE_ERROR.FILE_EXCEEDS_SIZE_LIMIT:
alert("上传文件超过限制（20M）！");
break;
case SWFUpload.QUEUE_ERROR.ZERO_BYTE_FILE:
case SWFUpload.QUEUE_ERROR.INVALID_FILETYPE:
default:
alert("文件出现错误！");
break;
}
} catch (ex) {
this.debug(ex);
}
}
// 文件选择完毕时触发
function fileDialogComplete(numFilesSelected, numFilesQueued) {
try {
if (numFilesQueued > 0) {
$("#divImgs").show();
for (var i = 0; i < numFilesQueued; i++) {
$("#ulUpload").append('<li id="li' + i + '"><img class="imgload" src="/style/image/loading.gif" alt="" /></li>');
}
this.startUpload();
}
} catch (ex) {
this.debug(ex);
}
}
// 滚动条的处理方法 暂时没写
function uploadProgress(file, bytesLoaded) {
}
// 每个文件上传成功后的处理
function uploadSuccess(file, serverData) {
try {
var index = file.id.substr(file.id.lastIndexOf('_') + 1);
$("#li" + index).html("");
$("#li" + index).html('<img src="' + serverData + '" alt=""/>');
index++;
} catch (ex) {
this.debug(ex);
}
}
// 上传完成后，触发下一个文件的上传
function uploadComplete(file) {
try {
if (this.getStats().files_queued > 0) {
this.startUpload();
}
} catch (ex) {
this.debug(ex);
}
}
// 单个文件上传错误时处理
function uploadError(file, errorCode, message) {
var imageName = "imgerror.png";
try {
var index = file.id.substr(file.id.lastIndexOf('_') + 1);
$("#li" + index).html("");
$("#li" + index).html('<img src="/style/image/imgerror.png" alt=""/>');
index++;
} catch (ex3) {
this.debug(ex3);
}
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div style="width: 600px;">
<div class="divTxt">
文本框
</div>
<div style="height: 30px; line-height: 30px;">
<div id="divBtn" style="float: left; width: 26px; height: 26px;">
</div>
<div style="float: right;">
<input id="btnReply" type="button" value="发表" />
</div>
</div>
<div id="divImgs" style="border: 1px solid #cdcdcd; display: none;">
<div>
上传图片</div>
<ul id="ulUpload" class="ulUpload">
</ul>
</div>
</div>
</form>
</body>
</html>
使用Vs2010开发，以下为
项目源码地址 
