Cakephp xml序列化不起作用

Question

使用XML序列化功能时，我遇到了以下错误。

Warning (2): get_class() expects parameter 1 to be object, array given [CORE/cake/libs/xml.php, line 208]

Fatal error: Call to undefined method Xml::addAttribute() in /usr/share/php/cake/libs/xml.php on line 283 

我已经复制粘贴了下面序列化的数组。

Array
(
    [0] => Array
        (
            [User] => Array
                (
                    [longitude] => 12
                    [latitude] => 1
                    [firstname] => Jae
                    [surname] => Choi
                    [profile_pic] => /img/files/test.jpeg
                    [facebook_id] => 12
                )

            [0] => Array
                (
                    [distance] => 0
                )

        )

    [1] => Array
        (
            [User] => Array
                (
                    [longitude] => 12
                    [latitude] => 1
                    [firstname] => 
                    [surname] => 
                    [profile_pic] => 
                    [facebook_id] => 13
                )

            [0] => Array
                (
                    [distance] => 0
                )

        )

    [2] => Array
        (
            [User] => Array
                (
                    [longitude] => -37.816
                    [latitude] => -37.811
                    [firstname] => Jae1
                    [surname] => Choi1
                    [profile_pic] => /img/files/test1.jpeg
                    [facebook_id] => 21
                )

            [0] => Array
                (
                    [distance] => 6679.12217489041
                )

        )

)

我不知道为什么我会收到这个错误。如果有人可以提供帮助，那将不胜感激。

谢谢。 宰