dropzone.js和ASP.NET MVC文件发布是否为空？

I am trying to use dropzone.js to upload images in my ASP.NET MVC app. I am able to set-up the dropzone programatically, click on it, select the image and when I click "Open" in the file dialog, the correct Action is hit in the controller. However, the HttpPostedFileBase always comes back as null so I can't do anything with the image. ON the client-side, however, it shows the image thumbnail correctly, eventhough I can't get it on the server side.I am trying to use dropzone.js to upload images