mvc Html.BeginForm和Ajax.BeginFrom表单提交

今天使用异步提交附件后台死活获取不到文件，代码还原

 1  @using (Ajax.BeginForm("Add", "Event",  new AjaxOptions() { HttpMethod = "Post", OnSuccess = "EntryFormJS.SubmitSuccess" }, new { id = "myform" }))
 2                 {
 3                     <div class="form-group">
 4                         <label for="name">标题</label>
 5                         <input type="text" class="form-control" id="title" name="title"
 6                                placeholder="请输入标题">
 7                     </div>
 8                     <div class="form-group">
 9                         <label for="inputfile">封面图</label>
10                         <input type="file" id="coverPic" name="coverPic">
11                     </div>
12                     <div class="form-group">
13                         <div class="form-group">
14                             <label for="name">内容</label>
15                             <textarea id="content" name="content" style="width:100%"></textarea>
16                         </div>
17                     </div>
18                     <input type="hidden" id="id" name="id" />
19                     <div>
20                         <button type="submit" class="btn btn-success" style="margin-left:200px">提交</button>
21                     </div>
22                 }

控制器使用   HttpPostedFileBase postedFile = Request.Files["coverPic"];接收数据，postedFile 值总是null。大脑暂时短路了，确实ajax提交表单中如果含有文件则无法获取。

后尝试使用jquery-form.js提交表单，后台获取到了附件。代码如下

html

 1  @using (Html.BeginForm("Add", "Event", FormMethod.Post, new { enctype = "multipart/form-data" }))
 2                 {
 3                     <div class="form-group">
 4                         <label for="name">标题</label>
 5                         <input type="text" class="form-control" id="title" name="title"
 6                                placeholder="请输入标题">
 7                     </div>
 8                     <div class="form-group">
 9                         <label for="inputfile">封面图</label>
10                         <input type="file" id="coverPic" name="coverPic">
11                     </div>
12                     <div class="form-group">
13                         <div class="form-group">
14                             <label for="name">内容</label>
15                             <textarea id="content" name="content" style="width:100%"></textarea>
16                         </div>
17                     </div>
18                     <input type="hidden" id="id" name="id" />
19                     <div>
20                         <button type="button" onclick="submitData()" class="btn btn-success" style="margin-left:200px">提交</button>
21                     </div>
22                 }

js

 1  var submitData = function () {
 2             var content = $("#title").val();
 3             if (content.trim().length == 0) {
 4                 $.notify({ message: "请输入标题！", status: ‘warning‘, timeout: 2000 }).show();
 5                 return false;
 6             }
 7             $(‘form‘).ajaxSubmit({
 8                 type: "post",
 9                 url: "/Event/Add",
10                 success: function (result) {
11                     if (!result.error) {
12                         $.notify({ message: "操作成功", status: ‘success‘, timeout: 2000 }).show();
13                         $(‘#eventModal‘).modal(‘hide‘)
14                         $("#tableList").bootstrapTable(‘refresh‘);
15                     }
16                     else
17                         $.notify({ message: result.msg, status: ‘warning‘, timeout: 2000 }).show();
18                 }
19             });
20         }