PHP一个比较完善的树形结构代码

<?php

/**
 * 通用的树型类，可以生成任何树型结构
 */
class tree
{
    /**
     * 生成树型结构所需要的2维数组
     * @var array
     */
    var $arr = array();

    /**
     * 生成树型结构所需修饰符号，可以换成图片
     * @var array
     */
    var $icon = array('│', '├', '└');

    /**
     * @access private
     */
    var $ret = '';

    /**
     * 构造函数，初始化类
     * @param array 2维数组，例如：
     * array(
     *      1 => array('id'=>'1','parentid'=>0,'name'=>'一级栏目一'),
     *      2 => array('id'=>'2','parentid'=>0,'name'=>'一级栏目二'),
     *      3 => array('id'=>'3','parentid'=>1,'name'=>'二级栏目一'),
     *      4 => array('id'=>'4','parentid'=>1,'name'=>'二级栏目二'),
     *      5 => array('id'=>'5','parentid'=>2,'name'=>'二级栏目三'),
     *      6 => array('id'=>'6','parentid'=>3,'name'=>'三级栏目一'),
     *      7 => array('id'=>'7','parentid'=>3,'name'=>'三级栏目二')
     *      )
     */
    function tree($arr = array())
    {
        $this->arr = $arr;
        $this->ret = '';
        return is_array($arr);
    }

    /**
     * 得到父级数组
     * @param int
     * @return array
     */
    function get_parent($myid)
    {
        $newarr = array();
        if (!isset($this->arr[$myid])) return false;
        $pid = $this->arr[$myid]['parentid'];
        $pid = $this->arr[$pid]['parentid'];
        if (is_array($this->arr)) {
            foreach ($this->arr as $id => $a) {
                if ($a['parentid'] == $pid) $newarr[$id] = $a;
            }
        }
        return $newarr;
    }

    /**
     * 得到子级数组
     * @param int
     * @return array
     */
    function get_child($myid)
    {
        $a = $newarr = array();
        if (is_array($this->arr)) {
            foreach ($this->arr as $id => $a) {
                if ($a['parentid'] == $myid) $newarr[$id] = $a;
            }
        }
        return $newarr ? $newarr : false;
    }

    /**
     * 得到当前位置数组
     * @param int
     * @return array
     */
    function get_pos($myid, &$newarr)
    {
        $a = array();
        if (!isset($this->arr[$myid])) return false;
        $newarr[] = $this->arr[$myid];
        $pid = $this->arr[$myid]['parentid'];
        if (isset($this->arr[$pid])) {
            $this->get_pos($pid, $newarr);
        }
        if (is_array($newarr)) {
            krsort($newarr);
            foreach ($newarr as $v) {
                $a[$v['id']] = $v;
            }
        }
        return $a;
    }


    /**
     * -------------------------------------
     *  得到树型结构
     * -------------------------------------
     * @author  Midnight(杨云洲),  yangyunzhou@foxmail.com
     * @param $myid 表示获得这个ID下的所有子级
     * @param $str 生成树形结构基本代码, 例如: "<option value=$id $select>$spacer$name</option>"
     * @param $sid 被选中的ID, 比如在做树形下拉框的时候需要用到
     * @param $adds
     * @param $str_group
     * @return unknown_type
     */
    function get_tree($myid, $str, $sid = 0, $adds = '', $str_group = '')
    {
        $number = 1;
        $child = $this->get_child($myid);
        if (is_array($child)) {
            $total = count($child);
            foreach ($child as $id => $a) {
                $j = $k = '';
                if ($number == $total) {
                    $j .= $this->icon[2];
                } else {
                    $j .= $this->icon[1];
                    $k = $adds ? $this->icon[0] : '';
                }
                $spacer = $adds ? $adds . $j : '';
                $selected = $id == $sid ? 'selected' : '';
                @extract($a);
                $parentid == 0 && $str_group ? eval("$nstr = "$str_group";") : eval("$nstr = "$str";");
                $this->ret .= $nstr;
                $this->get_tree($id, $str, $sid, $adds . $k . '&nbsp;', $str_group);
                $number++;
            }
        }
        return $this->ret;
    }

    /**
     * 同上一方法类似,但允许多选
     */
    function get_tree_multi($myid, $str, $sid = 0, $adds = '')
    {
        $number = 1;
        $child = $this->get_child($myid);
        if (is_array($child)) {
            $total = count($child);
            foreach ($child as $id => $a) {
                $j = $k = '';
                if ($number == $total) {
                    $j .= $this->icon[2];
                } else {
                    $j .= $this->icon[1];
                    $k = $adds ? $this->icon[0] : '';
                }
                $spacer = $adds ? $adds . $j : '';

                $selected = $this->have($sid, $id) ? 'selected' : '';
                //echo $sid.'=>'.$id.' : '.$selected.' . <br/>';
                @extract($a);
                eval("$nstr = "$str";");
                $this->ret .= $nstr;
                $this->get_tree_multi($id, $str, $sid, $adds . $k . '&nbsp;');
                $number++;
            }
        }
        return $this->ret;
    }

    function have($list, $item)
    {
        return (strpos(',,' . $list . ',', ',' . $item . ','));
    }
}