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以前，在頁面上實現縮略圖必須借助第三方組件。現在，有了.NET，就可以很輕松地實現縮略圖。下面就是實現縮略圖的例子。
ToThumbnailImage.aspx
<%@ Page language="c#" Codebehind="ToThumbnailImage.aspx.cs" Src="ToThumbnailImage.aspx.cs" AutoEventWireup="false"
Inherits="Exam_C.ToThumbnailImage" %>
<html>
<head>
<title>Lion互動網絡 =>生成縮略圖</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 的摘要說明。
/// </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 窗體設計器生成的代碼
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
//調用生成縮略圖方法
ToThumbnailImages("lionsky.jpg","b.gif",300);
}
#endregion
#region Helper
/// <summary>
/// 獲取圖像編碼解碼器的所有相關信息
/// </summary>
/// <param name="mimeType">包含編碼解碼器的多用途網際郵件擴充協議 (MIME) 類型的字符串</param>
/// <returns>返回圖像編碼解碼器的所有相關信息</returns>
static ImageCodecInfo GetCodecInfo(string mimeType)
{
ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
foreach(ImageCodecInfo ici in CodecInfo)
{
if(ici.MimeType == mimeType)return ici;
}
return null;
}
/// <summary>
/// 檢測擴展名的有效性
/// </summary>
/// <param name="sExt">文件名擴展名</param>
/// <returns>如果擴展名有效,返回true,否則返回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>
/// 保存圖片
/// </summary>
/// <param name="image">Image 對象</param>
/// <param name="savePath">保存路徑</param>
/// <param name="ici">指定格式的編解碼參數</param>
void SaveImage(System.Drawing.Image image,string savePath,ImageCodecInfo ici)
{
//設置 原圖片 對象的 EncoderParameters 對象
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>
/// 生成縮略圖
/// </summary>
/// <param name="sourceImagePath">原圖片路徑(相對路徑)</param>
/// <param name="thumbnailImagePath">生成的縮略圖路徑,如果為空則保存為原圖片路徑(相對路徑)</param>
/// <param name="thumbnailImageWidth">縮略圖的寬度（高度與按源圖片比例自動生成）</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("原圖片文件格式不正確,支持的格式有[ "+ AllowExt +"
]","SourceImagePath");
}
//從 原圖片 創建 Image 對象
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;
//計算圖片的比例
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 類的新實例
Bitmap bitmap = new Bitmap(ThumbnailImageWidth, num, PixelFormat.Format32bppArgb);
//從指定的 Image 對象創建新 Graphics 對象
Graphics graphics = Graphics.FromImage(bitmap);
//清除整個繪圖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繪制 原圖片 對象
graphics.DrawImage(image, new Rectangle(0, 0, ThumbnailImageWidth, num));
image.Dispose();
try
{
//將此 原圖片 以指定格式并用指定的編解碼參數保存到指定文件
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
}
}
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