如何在For循环下获得选择的多选择选择值

This is my view file code

这是我的视图文件代码

<?php for($i=0; $i<4; $i++)  { ?>
 <div class="box22">
      <div class="mcm">
           <input type="text" placeholder="Myself" id="coworkers" name="coworkers[]" />
           <span class="bar"></span>
      </div>

      <div class="select2">
       <select id="category_<?php echo $i; ?>" name="category[]" class="chosen-select ref-sel1" multiple >
           <?php
           foreach($genre as $gen){
                echo '<option value='.$gen->genre_id.'>'.$gen->genre_name.'</option>';
           } 
           ?>
       </select>
      </div>
 </div>
<?php } ?> 
<?php