PHP 获取数组任意下标key的上一个prev和下一个next下标值

<?php	
$xoops[1] = '小';
$xoops[2] = '孩';
$xoops[3] = '子';
$xoops[4] = '气';


$steps = new Steps();

foreach($xoops as $key=>$value){

$steps->add($key);

}

$steps->setCurrent(3);//参数为key值
echo '上一个下标：'.$steps->getPrev()."<br />";
echo '指定的下标：'.$steps->getCurrent()."<br />";
echo '下一个下标：'.$steps->getNext()."<br />";




class Steps {

 

    private $all;

    private $count;

    private $curr;

 

    function __construct() {

        $this->count = 0;

    }

    function add($step) {

        $this->count++;

        $this->all[$this->count] = $step;

    }

    function setCurrent($step) {

        reset($this->all);

        for ($i = 1; $i <= $this->count; $i++) {

            if ($this->all[$i] == $step)

                break;

            next($this->all);

        }

        $this->curr = current($this->all);

    }

    function getCurrent() {

        return $this->curr;

    }

    function getNext() {

        self::setCurrent($this->curr);

        return next($this->all);

    }

    function getPrev() {

        self::setCurrent($this->curr);

        return prev($this->all);

    }

}

上一个下标：2
指定的下标：3
下一个下标：4