//完整的目录结构
    function get_dir_tree($uid,$from_dir=0){
        $sql = "select dir_id,dir_name,depth,p_id from $this->_dir_table where user_id=$uid and is_del=0 and dir_id>=$from_dir";
        $res = $this->db->query($sql)->result_array();
        if(!isset($res[0])){
            return null;
        }
        $this->load->helper('array');
        //获取depth区间
        $max_depth = 0;
        foreach($res as $dps => $d){
            if($d['depth']>$max_depth){
                $max_depth = $d['depth'];
            }
        }
        for($i=$max_depth;$i>=0;$i--){ //处理成树形，子集存在child里,有没有自己看有没有child字段
            foreach($res as $key=>$val){
                if($val['depth']==$i){
                    foreach($res as $k=>$v){
                        if($val['p_id']==$v['dir_id']){
                            $v['child'][] = $val;
                            $res[$k] = $v;
                            unset($res[$key]);
                        }
                    }
                }
            }
        }
        $return =  $this->has_child_then_add_ul($res);
        $html="

            
            
全部文件
";
        $html.=$return."
";
        return $html;
    }
    private function has_child_then_add_ul($res,$html='',$collaps_times=1){
        $collaps = 15;//前端写的是m_l_15, m_l_30 这样的 , 15为一个单位，跟前端商定就好
        $indent = $collaps_times*$collaps;
        $has_sibling = 0;
        $ul_begin = "
";
        $ul_end = "
";
        $li_begin = "
%s
";//%s处是dir_name
        // $li_begin = "
%s";//%s处是dir_name
        $li_end = "
";
        $count_li_end = $count_ul_end = 0;
        foreach($res as $key=>$val){
            if(0==$key){
                $html.=$ul_begin;
            }
            $html.=sprintf($li_begin,$indent,$val['dir_name']);
            $count_li_end++;
            if(isset($val['child'])){
                $html = $this->has_child_then_add_ul($val['child'],$html,$collaps_times+1);
            }
            $html.=$li_end;
            if(!isset($res[$key+1])){
                $html.=$ul_end;
            }
        }
        return $html ;
    }