Я очень стараюсь, чтобы это работало, но я получаю сообщение об ошибке при загрузке файла.

ASPX

<asp:FileUpload ID="FileUpload1" runat="server" CssClass="file-upload-dialog" />
<asp:Button runat="server" ID="btnUpload" CssClass="btn upload" Text="Upload" />

Обработчик

public void ProcessRequest(HttpContext context)
      {
            context.Response.ContentType = "multipart/form-data";
            context.Response.Expires = -1;
            try
            {
                  HttpPostedFile postedFile = context.Request.Files["file"];
                  string savepath = HttpContext.Current.Server.MapPath("~/assets/common/CompetitionEntryImages/");
                  var extension = Path.GetExtension(postedFile.FileName);

                  if (!Directory.Exists(savepath))
                        Directory.CreateDirectory(savepath);

                  var id = Guid.NewGuid() + extension;
                  if (extension != null)
                  {
                        var fileLocation = string.Format("{0}/{1}",
                                                         savepath,
                                                         id);

                        postedFile.SaveAs(fileLocation);
                        context.Response.Write(fileLocation);
                        context.Response.StatusCode = 200;
                  }
            }
            catch (Exception ex)
            {
                  context.Response.Write("Error: " + ex.Message);
            }
      }

Jquery

$(document).ready(function () {
            email = $("input[id$='emailHV']").val();
            alert(email);
            $('#aspnetForm').attr("enctype", "multipart/form-data");
      });



$('#<%= btnUpload.ClientID %>').on('click', function (e) {
            e.preventDefault();
            var fileInput = $('#ctl00_PageContent_Signup_ctl06_MWFileUpload_FileUpload1');
            var fd = new window.FormData();
            fd.append('file', fileInput.files[0]);

            $.ajax({
                  url: '/charity-challenge/MWFileUploadHandler.ashx',
                  data: fd,
                  processData: false,
                  contentType: false,
                  type: 'POST',
                  success: function (data) {
                        alert(data);
                  }
            });
      });

Ошибка

HTML

<input type="file" name="ctl00$PageContent$Signup$ctl06$MWFileUpload$FileUpload1" id="ctl00_PageContent_Signup_ctl06_MWFileUpload_FileUpload1" class="file-upload-dialog">

 <input type="submit" name="ctl00$PageContent$Signup$ctl06$MWFileUpload$btnUpload" 
value="Upload" onclick="javascript:WebForm_DoPostBackWithOptions(new 
WebForm_PostBackOptions(&quot;ctl00$PageContent$Signup$ctl06$MWFileUpload$btnUpload&quot;, 
&quot;&quot;, true, &quot;&quot;, &quot;&quot;, false, false))" 
id="ctl00_PageContent_Signup_ctl06_MWFileUpload_btnUpload" class="button">

ПРАВКИ

Наконец, я заработал, выполнив эти действия для формирования данных.

var fileData = fileInput.prop("files")[0];   // Getting the properties of file from file field
        var formData = new window.FormData();                  // Creating object of FormData class
        formData.append("file", fileData); // Appending parameter named file with properties of file_field to form_data
        formData.append("user_email", email);

ПОЛНЫЙ РАБОЧИЙ КОД

$('#<%= btnUpload.ClientID %>').on('click', function (e) {
            e.preventDefault();
            var fileInput = $('#<%= FileUpload1.ClientID %>');
            var fileData = fileInput.prop("files")[0];   // Getting the properties of file from file field
            var formData = new window.FormData();                  // Creating object of FormData class
            formData.append("file", fileData); // Appending parameter named file with properties of file_field to form_data
            formData.append("user_email", email);
            $.ajax({
                  url: '/charity-challenge/MWFileUploadHandler.ashx',
                  data: formData,
                  processData: false,
                  contentType: false,
                  type: 'POST',
                  success: function (data) {
                        var obj = $.parseJSON(data);
                        if (obj.StatusCode == "OK") {
                              $('#<%= imagePath.ClientID %>').val(obj.ImageUploadPath);
                              $('.result-message').html(obj.Message).show();
                        } else if (obj.StatusCode == "ERROR") {
                              $('.result-message').html(obj.Message).show();
                        }
                  },
                  error: function (errorData) {
                        $('.result-message').html("there was a problem uploading the file.").show();
                  }
            });
      });