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(&#39;│&#39;,&#39;├&#39;,&#39;└&#39;);

/**
* @access private
*/
var $ret = &#39;&#39;;

/**
* 构造函数，初始化类
* @param array 2维数组，例如：
* array(
* 1 => array(&#39;id&#39;=>&#39;1&#39;,&#39;parentid&#39;=>0,&#39;name&#39;=>&#39;一级栏目一&#39;),
* 2 => array(&#39;id&#39;=>&#39;2&#39;,&#39;parentid&#39;=>0,&#39;name&#39;=>&#39;一级栏目二&#39;),
* 3 => array(&#39;id&#39;=>&#39;3&#39;,&#39;parentid&#39;=>1,&#39;name&#39;=>&#39;二级栏目一&#39;),
* 4 => array(&#39;id&#39;=>&#39;4&#39;,&#39;parentid&#39;=>1,&#39;name&#39;=>&#39;二级栏目二&#39;),
* 5 => array(&#39;id&#39;=>&#39;5&#39;,&#39;parentid&#39;=>2,&#39;name&#39;=>&#39;二级栏目三&#39;),
* 6 => array(&#39;id&#39;=>&#39;6&#39;,&#39;parentid&#39;=>3,&#39;name&#39;=>&#39;三级栏目一&#39;),
* 7 => array(&#39;id&#39;=>&#39;7&#39;,&#39;parentid&#39;=>3,&#39;name&#39;=>&#39;三级栏目二&#39;)
* )
*/
function tree($arr=array())
{
 $this->arr = $arr;
 $this->ret = &#39;&#39;;
 return is_array($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][&#39;parentid&#39;];
$pid = $this->arr[$pid][&#39;parentid&#39;];
if(is_array($this->arr))
{
foreach($this->arr as $id => $a)
{
if($a[&#39;parentid&#39;] == $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[&#39;parentid&#39;] == $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][&#39;parentid&#39;];
if(isset($this->arr[$pid]))
{
$this->get_pos($pid,$newarr);
}
if(is_array($newarr))
{
krsort($newarr);
foreach($newarr as $v)
{
$a[$v[&#39;id&#39;]] = $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 = &#39;&#39;, $str_group = &#39;&#39;)
{
$number=1;
$child = $this->get_child($myid);
if(is_array($child))
{
 $total = count($child);
foreach($child as $id=>$a)
{
$j=$k=&#39;&#39;;
if($number==$total)
{
$j .= $this->icon[2];
}
else
{
$j .= $this->icon[1];
$k = $adds ? $this->icon[0] : &#39;&#39;;
}
$spacer = $adds ? $adds.$j : &#39;&#39;;
$selected = $id==$sid ? &#39;selected&#39; : &#39;&#39;;
@extract($a);
$parentid == 0 && $str_group ? eval("$nstr = "$str_group";") : eval("$nstr = "$str";");
$this->ret .= $nstr;
$this->get_tree($id, $str, $sid, $adds.$k.&#39; &#39;,$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 = &#39;&#39;)
{
$number=1;
$child = $this->get_child($myid);
if(is_array($child))
{
 $total = count($child);
foreach($child as $id=>$a)
{
$j=$k=&#39;&#39;;
if($number==$total)
{
$j .= $this->icon[2];
}
else
{
$j .= $this->icon[1];
$k = $adds ? $this->icon[0] : &#39;&#39;;
}
$spacer = $adds ? $adds.$j : &#39;&#39;;

$selected = $this->have($sid,$id) ? &#39;selected&#39; : &#39;&#39;;
//echo $sid.&#39;=>&#39;.$id.&#39; : &#39;.$selected.&#39; . <br/>&#39;;
@extract($a);
eval("$nstr = "$str";");
$this->ret .= $nstr;
$this->get_tree_multi($id, $str, $sid, $adds.$k.&#39; &#39;);
$number++;
}
}
return $this->ret;
}

function have($list,$item){
return(strpos(&#39;,,&#39;.$list.&#39;,&#39;,&#39;,&#39;.$item.&#39;,&#39;));
}
}
?>