ASP.net WebAPI 上传图片

        [HttpPost]
        public Task<Hashtable> ImgUpload()
        {
            // 检查是否是 multipart/form-data
            if (!Request.Content.IsMimeMultipartContent("form-data"))
                throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
            //文件保存目录路径
            string SaveTempPath = "~/SayPlaces/" + "/SayPic/SayPicTemp/";
            String dirTempPath = HttpContext.Current.Server.MapPath(SaveTempPath);
            // 设置上传目录
            var provider = new MultipartFormDataStreamProvider(dirTempPath);
            //var queryp = Request.GetQueryNameValuePairs();//获得查询字符串的键值集合
            var task = Request.Content.ReadAsMultipartAsync(provider).
                ContinueWith<Hashtable>(o =>
                {
                    Hashtable hash = new Hashtable();
                    hash["error"] = 1;
                    hash["errmsg"] = "上传出错";
                    var file = provider.FileData[0];//provider.FormData
                    string orfilename = file.Headers.ContentDisposition.FileName.TrimStart('"').TrimEnd('"');
                    FileInfo fileinfo = new FileInfo(file.LocalFileName);                    
                    //最大文件大小
                    int maxSize = 10000000;
                    if (fileinfo.Length <= 0)
                    {
                        hash["error"] = 1;
                        hash["errmsg"] = "请选择上传文件。";
                    }
                    else if (fileinfo.Length > maxSize)
                    {
                        hash["error"] = 1;
                        hash["errmsg"] = "上传文件大小超过限制。";
                    }
                    else
                    {
                        string fileExt = orfilename.Substring(orfilename.LastIndexOf('.'));
                        //定义允许上传的文件扩展名
                        String fileTypes = "gif,jpg,jpeg,png,bmp";
                        if (String.IsNullOrEmpty(fileExt) || Array.IndexOf(fileTypes.Split(','), fileExt.Substring(1).ToLower()) == -1)
                        {
                            hash["error"] = 1;
                            hash["errmsg"] = "上传文件扩展名是不允许的扩展名。";
                        }
                        else
                        {
                            String ymd = DateTime.Now.ToString("yyyyMMdd", System.Globalization.DateTimeFormatInfo.InvariantInfo);
                            String newFileName = DateTime.Now.ToString("yyyyMMddHHmmss_ffff", System.Globalization.DateTimeFormatInfo.InvariantInfo);
                            fileinfo.CopyTo(Path.Combine(dirTempPath, newFileName + fileExt), true);
                            fileinfo.Delete();
                            hash["error"] = 0;
                            hash["errmsg"] = "上传成功";
                        }
                    }
                    return hash;
                });
            return task;
        }