Ajax上传文件到C#Action中

引用js文件包：jquery.form.js可以下载 http://malsup.com/jquery/form/#download

  <script src="script/jquery.form.js"></script>

  var formEle = $("#DefaultPicture_Create_Form");//一定要form.find不然与查询页面重复
                        var defaultPictureName = formEle.find("#DefaultPictureName").val().trim();
                        var defaultPictureID = formEle.find("#DefaultPictureID").val();
                        $("#DefaultPicture_Create_Form").ajaxSubmit({
                            url: "@Url.Action("Save", "DefaultPictureMaintenance")",
                            type: "post",
                            dataType: 'json',
                            data: {
                                DefaultPictureName: defaultPictureName,
                                DefaultPictureID: defaultPictureID
                            },
                            beforeSend: function () {
                                showLoading();
                            },
                            success: function (data) {
                                    debugger
                                if (data.Status == 200) {
                                    showOkClose(data.Message);
                                    closePopup();
                                    DefaultPictureSearch();
                                } else {
                                    showError(data.Message);
                                }
                        },
                            error: function (aa) {
                                debugger;
                            alert(aa);
                            },
                            complete: function () {
                                hideLoading();
                            }
                    });

   /// <summary>
        /// 将 Stream 转成 byte[]
        /// </summary>
        /// <param name="stream"></param>
        /// <returns></returns>

        private byte[] StreamToBytes(Stream stream)
        {
            byte[] bytes = new byte[stream.Length];
            stream.Read(bytes, , bytes.Length);
            // 设置当前流的位置为流的开始
            stream.Seek(, SeekOrigin.Begin);
            return bytes;
        }
        /// <summary>
        /// 检查文件是否合格，不合格返回错误信息，合格返回空字符
        /// </summary>
        /// <param name="file"></param>
        /// <returns></returns>
        private string CheckUploadFile(HttpPostedFileBase file)
        {
            //判断文件必须小于2M 格式必须PNG JPG
            if (file.ContentType != "image/png" && file.ContentType != "image/jpeg")
            {
              return  "Upload failed! Picture type can only be JPG or PNG.";
            }
            if (file.ContentLength /  >  * )
            {
                return"Upload failed! Image size can not be greater than 2M.";
            }
            return "";
        }
        public ActionResult Save(int DefaultPictureID, string DefaultPictureName, HttpPostedFileBase file)
        {
            bool isSaveSuccess = true;
            var DefaultPicture = new DefaultPictureItem();
            if (DefaultPictureID > )//编辑
            { //编辑时可以运行File为Null，表示用户没有修改图片
                var defaultPicModel = _defaultPictureService.GetByID(DefaultPictureID);//获取数据库中的
                defaultPicModel.DefaultPictureName = DefaultPictureName;
                defaultPicModel.UpdateBy = "testUser";
                defaultPicModel.UpdateDate = DateTime.Now;
                if (file!=null)
                {
                    //判断文件必须小于2M 格式必须PNG JPG
                    var errorMsg = CheckUploadFile(file);
                    if (!string.IsNullOrEmpty(errorMsg))
                    {
                        return Error(errorMsg);
                    }
                    var fileStream = file.InputStream;
                    defaultPicModel.DefaultPictureContent = StreamToBytes(fileStream);
                    DefaultPicture.DefaultPictureHaskKey = Guid.NewGuid().ToString();
                }
                isSaveSuccess = _defaultPictureService.Update(defaultPicModel);
            }
            else
            {//新增
                if (file == null)//新增的时候文件内容是必须得
                {
                    return Error("Upload failed! Image content can not be empty");
                }
                DefaultPicture.DefaultPictureName = DefaultPictureName;
                DefaultPicture.DefaultPictureHaskKey = Guid.NewGuid().ToString();
                DefaultPicture.CreateBy = "testUser";
                DefaultPicture.CreateDate = DateTime.Now;
                DefaultPicture.UpdateBy = "testUser";
                DefaultPicture.UpdateDate = DateTime.Now;
                //获取文件的内容
                //判断文件必须小于2M 格式必须PNG JPG
                var errorMsg = CheckUploadFile(file);
                if (!string.IsNullOrEmpty(errorMsg))
                {
                    return Error(errorMsg);
                }
                var fileStream = file.InputStream;
                DefaultPicture.DefaultPictureContent = StreamToBytes(fileStream);
                isSaveSuccess = _defaultPictureService.Update(DefaultPicture);
            }
            if (isSaveSuccess)
            {
                return Success("Save Success");
            }
            else
            {
                return Error("Save Failed");
            }
        }