细谈 Web Api 图片上传，在使用 Task.ContinueWith 变量无法赋值问题的解决办法！

在使用Asp.Net Web Api 图片上传接口的时候，到网上找了一些个例子，但大多数找到都是这个版本！

[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; 
}

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