通过Ajax / Angular调用时HttpContext.Current.Request.Files始终为null

Question

当HttpContext.Current.Session值即将到来时，通过ajax / angular调用时，HttpContext.Current.Request.Files始终为空

这是我通过ajax调用的代码。但是每次它都为空时。

[WebMethod]

public static string btnupldmem_Click(string flmem)
{

    string offr_login = HttpContext.Current.Session["offr_login"].ToString();
    if (offr_login != "")
    {
        HttpFileCollection uploadedFiles = HttpContext.Current.Request.Files;
        HttpPostedFile postedFile = HttpContext.Current.Request.Files["FileUpload"];
        if (postedFile != null && postedFile.ContentLength > 0)
        {
            //Save the File.
            string filePath = HttpContext.Current.Server.MapPath("~/Uploads/") + Path.GetFileName(postedFile.FileName);
            postedFile.SaveAs(filePath);
        }
    }
    return "success";
}

这是asp.net文件上传的前端代码。

<form action="/"  method="post" enctype="multipart/form-data">
  <td>
    <asp:Label ID="Label20"  runat="server" Text="Upload Memo Document"></asp:Label><span
    style="color: Red">*</span>
  </td>
  <td class="style2">
    <input type="file" name="FileUpload" />
    <asp:FileUpload ID="flmem" name="FileUpload"  onchange="angular.element(this).scope().fileNameChanged(this)" runat="server" CssClass="form-control" />

  </td>
  <td class="style2">
    <asp:Button ID="btnupldmem" ng-click="uploadclick()" runat="server" CssClass="btn btn-primary" Text="Upload"
    />
  </td>
  <td id="tdlnkmem" runat="server" visible="false">
    <asp:HyperLink ID="hypmem" runat="server" Target="_blank" Text="View" CssClass="btn btn-primary"></asp:HyperLink>
    <%--<asp:LinkButton ID="lnkmem" runat="server" OnClick="lnkmemupld_Click" Visible="false"></asp:LinkButton>--%>
  </td>
  <td id="tdlnkmemdel" runat="server" visible="false">
    <%-- <asp:LinkButton ID="lnkmemdel" runat="server" Text="Delete" OnClick="lnkmemdel_Click"
    Visible="false"></asp:LinkButton>--%>
    <asp:Button ID="lnkmemdel" runat="server" Text="Delete" OnClick="lnkmemdel_Click"
    CssClass="btn btn-primary" Visible="false" />
  </td>
  <td>
    <img id="imgload" src="../Return/load.jpg" style="display: none; height: 20px; width: 20px"
    alt="" />
  </td>
</form>