用C#轻松在DOTNET中实现缩略图

2022-07-15 80酷酷网 80kuku.com

　　缩略图以前，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-asohu.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

}
}