以前，在页面上实现缩略图必须借助第三方组件。现在，有了.NET，就可以很轻松地实现缩略图。下面就是实现缩略图的例子。
ToThumbnailImage.aspx
<%@ Page language="c#" Codebehind="ToThumbnailImage.aspx.cs" Src="ToThumbnailImage.aspx.cs" AutoEventWireup="false"
Inherits="Exam_C.ToThumbnailImage" %>
<html>
<head>
<title>Lion互动网络 =>生成缩略图</title>
</head>
<body>
<form id="Form1" method="post" runat="server">
</form>
</body>
</html>
ToThumbnailImage.aspx.cs
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Drawing.Imaging;
namespace Exam_C
{
/// <summary>
/// ToThumbnailImage 的摘要说明。
/// </summary>
public class ToThumbnailImage : System.Web.UI.Page
{
/*
Create By lion
2003-05-20 19:00
Copyright (C) 2004 www.LionSky.Net. All rights reserved.
Web: http://www.Lionsky.net ;
Email: lion-a@sohu.com
*/
static Hashtable htmimes = new Hashtable();
internal readonly string AllowExt = ".jpe|.jpeg|.jpg|.png|.tif|.tiff|.bmp";
#region Web 窗体设计器生成的代码
override protected void OnInit(EventArgs e)
{
#region htmimes[".jpe"]="image/jpeg";
htmimes[".jpeg"] = "image/jpeg";
htmimes[".jpg"] = "image/jpeg";
htmimes[".png"] = "image/png";
htmimes[".tif"] = "image/tiff";
htmimes[".tiff"] = "image/tiff";
htmimes[".bmp"] = "image/bmp";
#endregion
//调用生成缩略图方法
ToThumbnailImages("lionsky.jpg", "b.gif", 300);
}
#endregion
#region Helper
/// <summary>
/// 获取图像编码解码器的所有相关信息
/// </summary>
/// <param name="mimeType">包含编码解码器的多用途网际邮件扩充协议 (MIME) 类型的字符串</param>
/// <returns>返回图像编码解码器的所有相关信息</returns>
static ImageCodecInfo GetCodecInfo(string mimeType)
{
ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
foreach (ImageCodecInfo ici in CodecInfo)
{
if (ici.MimeType == mimeType) return ici;
}
return null;
}
/// <summary>
/// 检测扩展名的有效性
/// </summary>
/// <param name="sExt">文件名扩展名</param>
/// <returns>如果扩展名有效,返回true,否则返回false.</returns>
bool CheckValidExt(string sExt)
{
bool flag = false;
string[] aExt = AllowExt.Split('|');
foreach (string filetype in aExt)
{
if (filetype.ToLower() == sExt)
{
flag = true;
break;
}
}
return flag;
}
/// <summary>
/// 保存图片
/// </summary>
/// <param name="image">Image 对象</param>
/// <param name="savePath">保存路径</param>
/// <param name="ici">指定格式的编解码参数</param>
void SaveImage(System.Drawing.Image image, string savePath, ImageCodecInfo ici)
{
//设置 原图片 对象的 EncoderParameters 对象
EncoderParameters parameters = new EncoderParameters(1);
parameters.Param[0] = new EncoderParameter(Encoder.Quality, ((long)90));
image.Save(savePath, ici, parameters);
parameters.Dispose();
}
#endregion
#region Methods
/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="sourceImagePath">原图片路径(相对路径)</param>
/// <param name="thumbnailImagePath">生成的缩略图路径,如果为空则保存为原图片路径(相对路径)</param>
/// <param name="thumbnailImageWidth">缩略图的宽度（高度与按源图片比例自动生成）</param>
public void ToThumbnailImages(string sourceImagePath, string thumbnailImagePath, int thumbnailImageWidth)
{
string SourceImagePath = sourceImagePath;
string ThumbnailImagePath = thumbnailImagePath;
int ThumbnailImageWidth = thumbnailImageWidth;
string sExt = SourceImagePath.Substring(SourceImagePath.LastIndexOf(".")).ToLower();
if (SourceImagePath.ToString() == System.String.Empty) throw new NullReferenceException("SourceImagePath is null!");
if (!CheckValidExt(sExt))
{
throw new ArgumentException("原图片文件格式不正确,支持的格式有[ " + AllowExt + "]", "SourceImagePath");
}
//从 原图片 创建 Image 对象
System.Drawing.Image image = System.Drawing.Image.FromFile(HttpContext.Current.Server.MapPath(SourceImagePath));
int num = ((ThumbnailImageWidth / 4) * 3);
int width = image.Width;
int height = image.Height;
//计算图片的比例
if ((((double)width) / ((double)height)) >= 1.3333333333333333f)
{
num = ((height * ThumbnailImageWidth) / width);
}
else
{
ThumbnailImageWidth = ((width * num) / height);
}
if ((ThumbnailImageWidth < 1) || (num < 1))
{
return;
}
//用指定的大小和格式初始化 Bitmap 类的新实例
Bitmap bitmap = new Bitmap(ThumbnailImageWidth, num, PixelFormat.Format32bppArgb);
//从指定的 Image 对象创建新 Graphics 对象
Graphics graphics = Graphics.FromImage(bitmap);
//清除整个绘图面并以透明背景色填充
graphics.Clear(Color.Transparent);
//在指定位置并且按指定大小绘制 原图片 对象
graphics.DrawImage(image, new Rectangle(0, 0, ThumbnailImageWidth, num));
image.Dispose();
try
{
//将此 原图片 以指定格式并用指定的编解码参数保存到指定文件
string savepath = (ThumbnailImagePath == null ? SourceImagePath : ThumbnailImagePath);
SaveImage(bitmap, HttpContext.Current.Server.MapPath(savepath), GetCodecInfo((string)htmimes[sExt]));
}
catch (System.Exception e)
{
throw e;
}
finally
{
bitmap.Dispose();
graphics.Dispose();
}
}
#endregion
}
}