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 } }
