C#编写的生成缩略图程序

if(fileupload.PostedFile!=null)
     {    
      //addto为要添加的属性，aboutfile为文件说明
      string nam = fileupload.PostedFile.FileName ;
      //取得文件名(抱括路径)里最后一个"."的索引
      int i= nam.LastIndexOf(".");
      //取得文件扩展名
      string newext =nam.Substring(i);
      //这里我自动根据日期和文件大小不同为文件命名,确保文件名不重复
      DateTime now = DateTime.Now;
      string newname=now.DayOfYear.ToString()+fileupload.PostedFile.ContentLength.ToString();
      //保存文件到你所要的目录,这里是IIS根目录下的upload目录.你可以改变.
      //注意: 我这里用Server.MapPath()取当前文件的相对目录.在asp.net里""必须用"\"代替，把"upload\"改成"\upload\"就成了取当前文件的绝对目录了
      fileupload.PostedFile.SaveAs(Server.MapPath("upload\"+newname+newext));
      //得到这个文件的相关属性:文件名,文件类型,文件大小
      //fname.Text=myFile.PostedFile.FileName;
      //fenc.Text=myFile.PostedFile.ContentType ;
      //fsize.Text=myFile.PostedFile.ContentLength.ToString();
      //下面是生成缩略图
      System.Drawing.Image image,aNewImage;
      int width,height,newwidth,newheight;      
      image=System.Drawing.Image.FromFile(Server.MapPath("upload/"+newname.ToString()+newext.ToString()));
      System.Drawing.Image.GetThumbnailImageAbort callb =new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);    
      width=image.Width;
      height=image.Height;
      if(firstpageshow.SelectedValue.ToString()=="1"&&fenlei.SelectedValue.ToString()=="5")
      {
       newwidth=203;newheight=86;       
       newheight=height*newwidth/width;
      }
      else if(isweekman.SelectedValue.ToString()=="1")
      {
       newwidth=171;newheight=111;
       newheight=height*newwidth/width;
      }
      else if(firstpageshow.SelectedValue.ToString()=="1"&&fenlei.SelectedValue.ToString()=="3")
      {
       newwidth=171;newheight=111;
       newheight=height*newwidth/width;
      }
      else
      {
       newwidth=62;newheight=80;
       newheight=height*newwidth/width;
      }
      aNewImage=image.GetThumbnailImage(newwidth,newheight,callb,new System.IntPtr());
      aNewImage.Save(Server.MapPath("upload\"+"small_"+newname+newext));
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