File upload 空post值：CodeIgniter

通过codeigniter上载文件时，我遇到以下错误： 我的文件上载结果是：

我的控制器功能如下：

public function Upload files($data='')
    {   
        ini_set("display_errors",1); // I added so it would help me show errors
        error_reporting(E_ALL);

        print_r($_POST);exit('I am in the tp');
        $config['upload_path']          = 'assets/images/uploads/';
        //$config['allowed_types']        = 'gif|jpg|png';
        //$config['max_size']             = 100;
        //$config['max_width']            = 1024;
        //$config['max_height']           = 768;

        $this->load->library('upload', $config);
        $this->upload->initialize($config);

        if ( ! $this->upload->do_upload('userfile'))
        {
        $error = array('error' => $this->upload->display_errors());
        print_r($error);exit('The first loop'); 
        $this->load->view('upload_form', $error);
                }
         else
        {

        $data = array('upload_data' => $this->upload->data());
        print_r($data);exit();
        $this->load->view('upload_success', $data);
        }
    }

和我的视图文件：

                                <div id="Upload_div"> 
                                <?php //echo $error;?>   
                                <form action="<?php echo site_url() ?>/Admin/Upload_files/" method="POST" enctype="multipart/form-data">
                                  <label for="myfile">Select a file:</label>
                                  <input type="file" id="myfile" name="userfile"><br><br>
                                  <input type="submit" name="submit" value="submit">
                                </form>
                                </div>

$\u POST
不包含任何文件数据

拆下线路

 print_r($_POST);exit('I am in the tp');

然后告诉我们发生了什么。
嘿，我在检查了$\u帖子中的内容并修复了它之后，就可以解决这个问题了。非常感谢。