在symfony2控制器中将usort与关联数组一起使用

如何使用usort对symfony2控制器内的关联数组进行排序?

How can I use usort to sort an associative array inside a symfony2 controller?

//sort
function compare($a, $b)
{
    return strnatcmp($a['sort'], $b['sort']);
}

usort($content, 'compare');

这给了我以下错误:

警告:usort()期望参数2为有效的回调，找不到函数比较"或无效的函数名

Warning: usort() expects parameter 2 to be a valid callback, function 'compare' not found or invalid function name

就像将它放在自己的私有函数中一样

as does putting it in its own private function like this

// sort
usort($content, '$this->compare');

return $content;

}

//sort
private function compare($a, $b)
{
    return strnatcmp($a['sort'], $b['sort']);
}

这没变化

// sort 
usort($content, 'compare');

return $content;

}

//sort
private function compare($a, $b)
{
    return strnatcmp($a['sort'], $b['sort']);
}