如何将字节数组发送到webservice？我正在使用xamarin表格

Question

            -- xamarin forms code-- 
          public async void uploadimgAsync()
         {
          String pathofFile 
           ="/mnt/sdcard/Android/data/com.companyname.Lastappforcamera
            /files/Pictures/Sample/testone.jpg";

              using (var streamReader = new StreamReader(pathofFile))
            {
                var bytes = default(byte[]);

                using (var memstream = new MemoryStream())
                {
                    streamReader.BaseStream.CopyTo(memstream);

                    bytes = memstream.ToArray();
                }
              ax = bytes;

            }

            String URI = "xxxxxxxxx";

           await CrossFileUploader.Current.UploadFileAsync(URI, new 
            FileBytesItem("POST", ax, "testone.jpg"), new Dictionary<string, 
           string>()
                {
                   {"<HEADER KEY HERE>" , "<HEADER VALUE HERE>"}}
            );
           }

          --- web service method--- 

          [WebMethod]

       public String SaveDocumentPictureForXamarin(Byte[] 
       ImageByteArray,string ImageName)

        {
        string DocumentPath = Server.MapPath("~/Upload\\documents\\");

        if (!(Directory.Exists(DocumentPath)))
        {
            Directory.CreateDirectory(DocumentPath);
        }

         DocumentPath += ImageName; 

        FileStream objfilestream = new FileStream(DocumentPath, 
        FileMode.Create,FileAccess.ReadWrite);

        objfilestream.Write(ImageByteArray, 0, ImageByteArray.Length);

        objfilestream.Close();
        return "success";
         }  

内容类型：application / x-www-form-urlencoded

请帮我将图像作为bytearray上传到网络服务。我无法获取要上传的代码。我试过httpclient，它显示了web方法错误。我需要传递图像名称和imagebytearray。我是xamarin的新手。