xml方式封装通信数据方法

public static function xmlToEncode($data) {

    $xml = "";

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

        $attr = "";

        if(is_numeric($key)) {

            $attr = " id='{$key}'";

            $key = "item";

        }

        $xml .= "<{$key}{$attr}>";

        $xml .= is_array($value) ?

self::xmlToEncode($value) : $value;

        $xml .= "</{$key}>\n";

    }

    return $xml;

}