$_FILES 返回 null 数组

Question

我有一个像

<div class="body">
    <form action="<?php echo base_url();?>gallery/image_upload" id="myDropzone" class="dropzone" method="post" enctype="multipart/form-data">
        <div class="dz-message">
            <div class="drag-icon-cph">
                <i class="material-icons">touch_app</i>
            </div>
            <h3>Drop files here or click to upload.</h3>
            <em>(Choose image or drop file <strong>to</strong> upload.)</em>
        </div>
        <div class="fallback">
            <input name="file" type="file" multiple />
        </div>

         <div class="row clearfix">
            <div class="body">
                <div class="col-lg-12 col-md-12 col-sm-12 col-xs-12 text-center">
                   <a href="<?php echo base_url();?>gallery" class="btn btn-primary">REFRESH</a>
                   <input type="submit" class="btn btn-primary" value="UPLOAD">
                </div>
            <div class="body">
        </div>

    </form>
</div>

我有 controller 命名站点，我设置路由

$route['gallery/image_upload']='Site/gallery_upload/';

我在我的网站 controller 中有 gallery_upload function

public function gallery_upload(){
    print_r($_FILES);exit;
}

但它给了我 null 阵列