asp.net mvc ajax FileUpload

//后台代码
  [HttpPost]
        public ActionResult CreateCategory(HttpPostedFileBase file)
        {
            string url = Upload(file);
            if(url== "empty")
            {
                return Json("{state:fault}");
            }
            factory.Endpoint.Behaviors.Add(new WebHttpBehavior());
            var proxy = factory.CreateChannel();
            //用户组请求类
            ServicePostRequest<Guoany_Ga_B2BGCategory_InsertOrUpdate_Request> request = new ServicePostRequest<Guoany_Ga_B2BGCategory_InsertOrUpdate_Request>();
            request.ExtraData = new Guoany_Ga_B2BGCategory_InsertOrUpdate_Request();
            request.ExtraData.Parent_Id = "";
            request.ExtraData.Creater = "";
            request.ExtraData.Creattime = DateTime.Now;
            request.ExtraData.Des = "";
            request.ExtraData.Category_Id = Guid.NewGuid().ToString();
            request.ExtraData.Category_Name = "";
            request.ExtraData.Category_Url = url;
            request.ExtraData.Is_del = false;
            request.ExtraData.Is_show = true;
            request.ExtraData.Is_Special = false;
            request.ExtraData.Sort_No = 1;
            ServicePostResponse<Guoany_Ga_B2BGCategory_InsertOrUpdate_Response> response = proxy.InsertOrUpdateB2B_G_Category(request);
            //  ViewData["Group_Response"] = response.Data;
            bool result = response.Success;

            return Json("{state:success}");
        }
        public string Upload(HttpPostedFileBase file)
        {
            if (file == null)
            {
                return "empty";
            }
            var fileName = Path.Combine(Request.MapPath("~/Upload"), Path.GetFileName(file.FileName));

            if (Directory.Exists(Server.MapPath("~/Upload")) == false)//如果不存在就创建file文件夹
            {
                Directory.CreateDirectory(Server.MapPath("~/Upload"));
            }
            file.SaveAs(fileName);
            return "upload/"+Path.GetFileName(file.FileName);
        }
//-----------------------------------------------------------------------------------------
//前台代码

@{
    ViewBag.Title = "类别列表";
}

<script type="text/javascript">
    $(function () {
        var pager = $('#dg').datagrid().datagrid('getPager');    // get the pager of datagrid
        pager.pagination({
            buttons: [{
                iconCls: 'icon-search',
                handler: function () {
                    $('#dg').datagrid("reload");
                }
            }, {
                iconCls: 'icon-add',
                handler: function () {
                    alert('add');
                }
            }, {
                iconCls: 'icon-edit',
                handler: function () {
                    alert('edit');
                },
                iconCls: 'icon-remove',
                handler: function () {
                    alert('删除');
                }
            }]
        });

    })
    function searchCategory() {
        var stopOrenable = $('#stopOrenable').combobox('getValue');
        var txtCategoryName = $("#txtCategoryName").val();
        var showOrNot = $("#showOrNot").is(":checked") == true ? 1 : 0;
        var specilCategory = $("#specilCategory").is(":checked") == true ? 1 : 0;

        $('#dg').datagrid('load', {
            queryParams: {
                stopOrenable: stopOrenable,
                txtCategoryName: txtCategoryName,
                showOrNot: showOrNot,
                specilCategory: specilCategory

            }

        });
        //var randnum = Math.floor(Math.random() * 1000000);
        //alert(randnum)
        //var urls = '/Category_Manage/GetCategoryJsonList?randnum=' + randnum;

    }
    function addCategory() {
        $('#dd').dialog('open');

    }

    function editCategory() { }

    function showCategory() { }

    function hidenCategory() { }

    function enabledCategory() { }

    function stopCategory() { }
</script>

<script type="text/javascript">
    function PreviewImage(imgFile) {
        var filextension = imgFile.value.substring(imgFile.value.lastIndexOf("."), imgFile.value.length);
        filextension = filextension.toLowerCase();
        if ((filextension != '.jpg') && (filextension != '.gif') && (filextension != '.jpeg') && (filextension != '.png') && (filextension != '.bmp')) {
            alert("对不起，系统仅支持标准格式的照片，请您调整格式后重新上传，谢谢 !");
            imgFile.focus();
        }
        else {
            var path;
            if (document.all)//IE
            {
                imgFile.select();
                path = document.selection.createRange().text;

                document.getElementById("imgPreview").innerHTML = "";
                document.getElementById("imgPreview").style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(enabled='true',sizingMethod='scale',src=\"" + path + "\")";//使用滤镜效果
            }
            else//FF
            {
                path = window.URL.createObjectURL(imgFile.files[0]);
                var i = 0;
                i++;
                $("#imgPreview").append("<img id='img" + i + "'  width='120px' height='100px' src='" + path + "'/>");

            }
        }
    }
    function submitContent()
    {
        var formData = new FormData();
        var file = document.getElementById("upload").files[0];
        formData.append("file", file);
        $.ajax({
            type: "POST",
            url: '@Url.Action("CreateCategory", "Category_Manage")',
            data: formData,
            dataType: 'json',
            contentType: false,
            processData: false,
            success: function (response) {
                alert("sucess");
              },
            error: function (error) {
                alert("fault");
            }
        });
    }

</script>
<table id="dg" class="easyui-datagrid" title="商品类别列表" style="width:100%;height:250px"
       data-options="rownumbers:true,singleSelect:true,url:'/Category_Manage/GetCategoryJsonList',method:'get',toolbar:'#tb',footer:'#ft',pagination:true">
    <thead>
        <tr>
            <th data-options="field:'ParentCategoryName',width:80">上级类目</th>
            <th data-options="field:'Category_Name',width:100">类目名称</th>
            <th data-options="field:'Is_Del',width:80,align:'right'">启用状态</th>
            <th data-options="field:'Des',width:80,align:'right'">描述</th>
            <th data-options="field:'Is_Special',width:240">是否特殊项目</th>
            <th data-options="field:'Is_show',width:60,align:'center'">展示状态</th>
            <th data-options="field:'Sort_No',width:60,align:'center'">排序</th>

        </tr>
    </thead>
</table>
<div id="tb" style="padding:2px 5px;">
    <div>
        <input type="button" value="新增" onclick="addCategory()" />
        <input type="button" value="编辑" onclick="editCategory()" />
        <input type="button" value="展示" onclick="showCategory()" />
        <input type="button" value="隐藏" onclick="hidenCategory()" />
        <input type="button" value="启用" onclick="enabledCategory()" />
        <input type="button" value="停用" onclick="stopCategory()" />
    </div>
    类目名称 <input id="txtCategoryName" style="width:110px">
    是否停用
    <select id="stopOrenable" class="easyui-combobox" panelHeight="auto" style="width:100px">
        <option value="1">是</option>
        <option value="0">否</option>
    </select>
    <input type="checkbox" id="specilCategory" /> 特殊类目 <input type="checkbox" id="showOrNot" /> 是否展示
    <a href="#" id="search" class="easyui-linkbutton" onclick="searchCategory()" iconCls="icon-search">搜索</a>
</div>
<div id="dd" class="easyui-dialog" title="新增/编辑"
     data-options="iconCls:'icon-save',closed:true,modal: true,cache: false" style="width:800px;height:600px;padding:10px">
    @using (Html.BeginForm("CreateCategory", "Category_Manage", FormMethod.Post, new { enctype = "multipart/form-data" }))
    {
        <table style="border:1px solid ;width:700px;height:500px;">
            <tr>
                <td>父类目:<input type="text" /></td>
                <td colspan="2">
                    图片上传:<input type="file" name="file" style="width: 200px; height: 20px;" onchange="PreviewImage(this)" id="upload" />
                    <div id="imgPreview" style="width:120px; height:100px;margin-left: 280px;"></div>

                </td>

            </tr>
            <tr><td>类目:<input type="text" /></tr>
            <tr><td>是否特殊类目:<input type="checkbox" /></td><td>是否显示:<input type="checkbox" /></td></tr>
            <tr><td rowspan="1">类描述<textarea rows="2"></textarea></td></tr>
            <tr><td rowspan="1"><input onclick="submitContent()" value="提交" /></td></tr>
        </table>

    }
</div>