输入 mp3 文件返回 0

Question

当我尝试输入mp3文件时，$_FILES返回null.控制器：$audio = $_FILES['muziek']['tmp_name'];if ($audio != ''){     $audioContent = file_get_contents($audio);     $this->load->model('muziek_model');     $this->muziek_model->insertMuziek($audioContent);}var_dump($audio);var_dump($audioContent);看法：<?php echo form_open_multipart('Muziek/uploadMuziek');?><table>    <tr>        <td><?php echo form_label('MP3 Bestand:', 'muziek'); ?></td>        <td><input type="file" name="muziek" id="muziek" accept=".mp3" style="margin-left: 10px; padding-bottom: 35px; color: black" class="btn btn-login form-control login-formcontrol bg-white"/></td>    </tr>    <tr>        <td></td>        <td>            <?php echo form_submit('knop', 'Uploaden', 'class = "btn btn-login login-formcontrol"'); ?>        </td>    </tr></table><?php echo form_close();?>当我选择一个 mp3 文件时，音频不应为空