Request.files returns null after adding onsubmit attribute to the BeginForm  and working fine when removed . I tried with id attribute same issue.
also i tried to add from collection in the controller
view
@using (Html.BeginForm("Create", "Candidate", FormMethod.Post, new { onsubmit = "return SubmitForm(this)",  enctype = "multipart /form-data" }))
{
    <div class="form-horizontal">
       ....
        <div class="form-group">
            @Html.Label("Avatar", new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                <input type="file" name="file" multiple="multiple" />
            </div>
        </div>
        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </div>
    </div>
}
   
 function SubmitForm(form) {
            $.validator.unobtrusive.parse(form);
            if($(form).valid()){
                $.ajax({
                    type : "POST",
                    url : form.action,
                    data : $(form).serialize(),
                    success : function (data) {
                        if(data.success)
                        {
                            Popup.dialog('close');
                            dataTable.ajax.reload();
                            $.notify(data.message,{
                                globalPosition :"top center",
                                className : "success"
                            })
                        }
                    }
                });
            }
            return false;
        }
actionResult Create(model model)
{
}
 
    