（12）改变图片的大小生成缩略图

问题

你允许用户上传一个图片，但是传统的来说，这个图片一般是从一个camera输出的，这个图片太大。所以你想展现一个简单的图片或者缩略图。在你的网站允许用户在他看到完整图片之前先预览缩略图（译者：这是一个很好的用户体验）。

解决方案

使用以下几个类去更新现有的文件上传功能去调整图片：FileStream, Image, Bitmap,和Graphics 类去指定宽度和高度。

讨论

在下面的例子，以前创建的FileUpload类将得到更新和重组。创建一个新的功能，称为ResizeImage执行调整图片大小。调整大小后的图像将被保存在以前的文件夹的子文件夹中，名为（thumbnail）缩略图。 DeleteFile函数也被更新，同时删除缩略图和原始图像，并创建一个新的函数，并调用了两次删除功能 为了避免重复代码。下面是FileUpload类的代码：

译者：下边标红的代码是我加上去的。这样我们可以把图片和缩略图存到我们项目的文件夹下。否则他会存到：C:Program FilesCommon FilesMicrosoft SharedDevServer10.0目录下。

双击代码全选

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using System; using System.Collections.Generic; using System.Drawing; using System.Drawing.Drawing2D; using System.Linq; using System.Web; using System.IO;   namespace MvcApplication.Utils {     public static class FileUpload     {         public static char DirSeparator = Path.DirectorySeparatorChar;         public static string FilesPath = HttpContext.Current.Server.MapPath(string.Format("Content{0}Uploads{1}", DirSeparator, DirSeparator));         public static string UploadFile(HttpPostedFileBase file)         {             // Check if we have a file             if (null == file) return "";             // Make sure the file has content             if (!(file.ContentLength > 0)) return "";             string fileName = file.FileName;             string fileExt = Path.GetExtension(file.FileName);             // Make sure we were able to determine a proper             // extension             if (null == fileExt) return "";             // Check if the directory we are saving to exists             if (!Directory.Exists(FilesPath))             {                 // If it doesn't exist, create the directory                 Directory.CreateDirectory(FilesPath);             }             // Set our full path for saving             string path = FilesPath + DirSeparator + fileName;             // Save our file             file.SaveAs(Path.GetFullPath(path));             // Save our thumbnail as well             ResizeImage(file, 150, 100);             // Return the filename             return fileName;         }         public static void DeleteFile(string fileName)         {             // Don't do anything if there is no name             if (fileName.Length == 0) return;             // Set our full path for deleting             string path = FilesPath + DirSeparator + fileName;             string thumbPath = FilesPath + DirSeparator +             "Thumbnails" + DirSeparator + fileName;             RemoveFile(path);             RemoveFile(thumbPath);         }         private static void RemoveFile(string path)         {             // Check if our file exists             if (File.Exists(Path.GetFullPath(path)))             {                 // Delete our file                 File.Delete(Path.GetFullPath(path));             }         }         public static void ResizeImage(HttpPostedFileBase file, int width, int height)         {               string thumbnailDirectory =             String.Format(@"{0}{1}{2}", FilesPath,             DirSeparator, "Thumbnails");             // Check if the directory we are saving to exists             if (!Directory.Exists(thumbnailDirectory))             {                 // If it doesn't exist, create the directory                 Directory.CreateDirectory(thumbnailDirectory);             }             // Final path we will save our thumbnail             string imagePath =             String.Format(@"{0}{1}{2}", thumbnailDirectory,             DirSeparator, file.FileName);             // Create a stream to save the file to when we're             // done resizing             FileStream stream = new FileStream(Path.GetFullPath(             imagePath), FileMode.OpenOrCreate);             // Convert our uploaded file to an image             Image OrigImage = Image.FromStream(file.InputStream);             // Create a new bitmap with the size of our             // thumbnail             Bitmap TempBitmap = new Bitmap(width, height);             // Create a new image that contains quality             // information             Graphics NewImage = Graphics.FromImage(TempBitmap);             NewImage.CompositingQuality =             CompositingQuality.HighQuality;             NewImage.SmoothingMode =             SmoothingMode.HighQuality;             NewImage.InterpolationMode =             InterpolationMode.HighQualityBicubic;             // Create a rectangle and draw the image             Rectangle imageRectangle = new Rectangle(0, 0,             width, height);             NewImage.DrawImage(OrigImage, imageRectangle);             // Save the final file             TempBitmap.Save(stream, OrigImage.RawFormat);             // Clean up the resources             NewImage.Dispose();             TempBitmap.Dispose();             OrigImage.Dispose();             stream.Close();             stream.Dispose();         }     } }

 

上边的例子做了很多事，特别是在ResizeImage函数。

首先，如果缩略图​​目录不存在，它将被创建。接下来，一个新的FileStream会根据缩略图存放的完整路径被创建用于编辑。 原上传的图像根据uploaded的InputStream被转换为Image类的对象。一个新的位图会被根据图图像的宽度和高度创建。接下来用这个位图去创建一个新的Graphics对象。Graphics对象，NewImage，用于设置和定义质量，表面光滑，插补模式。如果没有这些设置，缩略图会不会好看非常像素化和调整笨拙。

一旦都设置好了，一个新的矩形被创建并且原始图像被画到Graphics中。这是执行实际的调整大小。最后保存位图和所有创建的对象的处置，以释放资源。