我怎样才能在购物车中获得我的下拉菜单的价值？ 总是零

this is my view

 <?php foreach ($cart as $item): ?>
                                    <tr>
                                        <td><?php echo $item['name']; ?></td>
                                        <td><?php echo $item['qty']; ?></td>
                                        <td><?php echo number_format($item['subtotal'],2); ?></td>
                                        <?php echo form_open_multipart('site/confirmed') ?>
                                        <?php
                                                $option = array();
                                                foreach($instructor as $r){
                                                $option[$r->id] = $r->instructor;
                                                }
                                                echo "<td>" . form_dropdown('instructor', $option) . "</td>";

                                                ?>

this is my model

            'isbn' => $items['name'],
            'price' =>  $items['price'],
            'instructor' =>  $this->input->post('instructor'),
            'qty' =>  $items['qty'],

when i use $this->input->post('instructor'), i always get zero.. help me please thanks in advance

Try this in your view :

<?php echo form_dropdown('instructor', $option, $this->input->post('instructor') ? $this->input->post('instructor') : $r->instructor); ?>