图片重新定义大小保存……

public class UploadPic
    {
        public UploadPic()
        {
        }

        /**//// <summary>
        /// 保存的方法
        /// </summary>
        /// <param name="_file">上传文件的方法</param>
        /// <param name="_compress">是否压缩图片，true的时候_minwidth和_minhight属性才有效</param>
        /// <param name="_saveOriginally">是否保存原始图片</param>
        /// <param name="_path">上传的路径</param>
        /// <param name="_minwidth">最小宽度（压缩的时候才有用）</param>
        /// <param name="_minhight">最小高度（压缩的时候才有用）</param>
        /// <returns>错误返回""，否则返回文件名</returns>
        public string Save(HtmlInputFile _file,bool _compress,bool _saveOriginally,string _path,int _minwidth,int _minhight)
        {
            string strFileName = "";

            //先检查文件名
            strFileName = CheckFile(_file);

            if(strFileName == "")
                return "";
            else
                strFileName = composeFileName(strFileName);//文件名通过检查后再组合成新文件名。
    
            try
            {
                System.Web.UI.Page MyPage = new Page();
                //如果不压缩，或者 压缩并且要求保存原文件，则保存原图片
                if(!_compress || (_compress && _saveOriginally))
                    _file.PostedFile.SaveAs(MyPage.Server.MapPath(_path + "max" + strFileName));
    
                //如果压缩，则保存压缩后的小图片
                if(_compress)
                {
                    System.Drawing.Image NewPic = System.Drawing.Image.FromStream(_file.PostedFile.InputStream);
                    
                    int intMaxHight = NewPic.Height;
                    int intMaxWidth = NewPic.Width;

                    if(intMaxHight <= _minhight && intMaxWidth <= _minwidth)
                    {
                        _minhight = intMaxHight;
                        _minwidth = intMaxWidth;
                    }
                    else
                    {
                        if(intMaxWidth>intMaxHight)
                        {
                            int tmpheight =(int)((double)intMaxHight/(double)intMaxWidth*(double)_minwidth);
                            _minhight = tmpheight > _minhight ? _minhight : tmpheight;
                        }
                        else
                        {
                            int tmpwidth =(int)((double)intMaxWidth/(double)intMaxHight*(double)_minhight);
                            _minwidth = tmpwidth > _minwidth ? _minwidth : tmpwidth;
                        }
                    }
                    System.Drawing.Image thumimg = null;
                    System.Drawing.Image.GetThumbnailImageAbort callb = new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);   
                    thumimg = NewPic.GetThumbnailImage(_minwidth,_minhight,callb,IntPtr.Zero); 
                    thumimg.Save(MyPage.Server.MapPath(_path + "min" + strFileName));    
                }
            }
            catch
            {
                strFileName="";
            }
            
            return strFileName;
        }

        /**//// <summary>
        /// 组合文件名
        /// </summary>
        /// <param name="_filename">原文件名</param>
        /// <returns>组合后的文件名</returns>
        private string composeFileName(string _filename)
        {    
            //组合文件名，文件名前加日期
            string date = DateTime.Now.ToString();
            date = date.Replace(":","");
            date = date.Replace(" ","");
            date = date.Replace("-","");

            return date + "_"+ _filename;
        }

        /**//// <summary>
        /// 检查文件格式
        /// </summary>
        /// <param name="_file">文件格式，这里定义的合法的是.jpg .gif两种</param>
        /// <returns>错误返回“”，正确返回文件名filename</returns>
        private string CheckFile(HtmlInputFile _file)
        {
            if(_file.PostedFile.ContentLength == 0)
                return "";

            string _strFile = _file.Value;
            string StrFileName = _strFile.Substring(_file.PostedFile.FileName.LastIndexOf(@"\")+1);
            string fileFormater = _strFile.Substring(_file.PostedFile.FileName.LastIndexOf("."));
            
            switch(fileFormater.ToLower())
            {
                case ".jpg":
                    return StrFileName;
                case ".gif":
                    return StrFileName;
                default:
                    return "";
            }
        }

        private bool ThumbnailCallback()
        {
            return false;
        }
    }