codeigniter分页下拉选择过滤器

我创建了一个网站，在这里我将项目分组。当用户从提供的下拉菜单中选择一个项目并提交时，与该项目编号相关的项目将被检索并发送回控制器。

我的控制器

public function dwg_list()
{
    $data['proj_num'] = $this->model_proj->proj_num_all();
    $num_row = 1;
    if ($this->input->post('project_no') != '0')
    {
        $data['result'] = $this->model_issue->list_dwg($this->input->post('project_no'));
        if (count($data['result']) > 0)
        {
            $num_row = count($data['result']);
        } else $num_row = 1;
    }
    $this->load->library('pagination');
    $config['base_url'] = base_url() . '/index.php/dwg_issue/dwg_list/page';
    $config['total_rows'] = $num_row;
    $config['per_page'] = 2; 
    $this->pagination->initialize($config); 

    $data['main_content'] = 'dwg_list';
    $this->load->view('includes/template.php', $data);
}

我的视图

<h1>This page displays all the registered drawings</h1>
<br>
<div id="body">
<div class="row">
        <div class="form-group-sm"><lable class="col-sm-2 control-label">Project number:</lable>
    <?php
        $js = 'onchange="this.form.submit()" class="form-control" id="focusInput"';
        echo form_open('dwg_issue/dwg_list');
        echo "<div class='"col-xs-2'">" . form_dropdown('project_no',$proj_num, $this->input->post('project_no'),$js)."</div>";
        echo form_error('project_no', '<div class="col-xs-4"><div class="alert alert-danger fade in"><a href="#" class="close" data-dismiss="alert" aria-label="close">&times;</a>','</div></div>');
    ?>
        </div>
        </div>
        <br>
<?php
echo "<noscript>".form_submit('submit','Submit')."</noscript>";
?>
        <table title="List of drawings" class="table table-hover" style="font-size: 14px">
            <caption><b>List of drawings</b></caption>
        <thead>
            <tr><th>Project number</th><th>Drawing number</th><th>Client drawing number</th>
                <th>Title</th><th>Size</th><th>Drawn by</th><th>Revision</th><th>Drawn Date</th></tr>
        </thead>    
        <tbody> &nbsp;
        <?php
            if(!empty($result))
            {
                foreach($result as $row)
                { 
                    echo "<tr>";
                    echo "<td>" . $row->project_no . "</td>";
                    echo "<td>" . $row->sws_dwg_no . "</td>";
                    echo "<td>" . $row->client_dwg_no . "</td>";
                    echo "<td>" . $row->dwg_title . "</td>";
                    echo "<td>" . $row->dwg_size . "</td>";
                    echo "<td>" . $row->dwg_by . "</td>";
                    echo "<td>" . $row->dwg_rev . "</td>";
                    echo "<td>" . date('Y/m/d', strtotime($row->dwg_date)) . "</td>"; 
                    echo "</tr>";
                }
            }
        ?>
        </tbody>
       </table>
       <?php echo $this->pagination->create_links(); ?>
</div>

我看到的问题是，当我单击下一个页码时，页面被刷新，下拉选择返回到默认值，然后提交给控制器。控制器无法向模型提交任何要从数据库中检索的内容。

那么我该如何克服这个问题呢。