表格延迟执行时

Question

您好我在PHP框架Codeigniter中有一个带有选择器名称“top”的表单。当我提交表单时，输入帖子不显示发布的值。只有当我第二次提交时，才会发布价值。代码如下，请指教？

<div id="selector_form">
<?php
echo form_open(base_url().'home/choose_car/'); ?>   
<select name="select_car">
<option>Please Select Car</option>
<?php   
    foreach ($list as $key => $value) {
            if($value->model == $car[0]->model){
                $selected = 'selected';
            }else{
                $selected = '';
            }
            //change make to carid
            echo "<option ".$selected." value='".$value->carID."''>".$value->make." - ".$value->model."</option>";
    }
?>  
</select>
<textarea id="description" rows="4" cols="50" ><?php if(isset($car)&&$car){print_r($car[0]->desc);}else{echo "Please Select Car";} ?></textarea>
<input type="submit" />
</div><!-- end selector_form -->
<table id="controls_table">
    <th>Section</th><th>Material</th><th>Color</th><th>Show</th>
    <tr>
    <td><label for="top">Top: </label></td>
    <td><select name="top">
    <?php
    if($material){
        foreach ($material as $key => $value) {
            if($value->materialID == $this->input->post('top')){
                $selected = 'selected';
            }else{
                $selected = '';
            }
            echo "<option ".$selected." value='".$value->materialID."'>Carbon/".$value->materialName."</option>";
        }
    }else{
        echo "<option ".$selected." >Please Select Car</option>";
    }
    ?>
    </select></td>