作者：老葛，北京亚艾元软件有限责任公司，http://www.yaiyuan.com
这是我们这里实际执行的语句。用来合成页面的是drupal_render_page函数。这个时候，传递过来的$page_callback_result，只是一个包含节点对象的呈现数组，节点外面的区域、区块是怎么加进来的呢？这是很多初学者的疑问。让我们来看这个函数的定义：
/**
* Renders the page, including all theming.
*
* @param $page
* A string or array representing the content of a page. The array consists of
* the following keys:
* - #type: Value is always 'page'. This pushes the theming through
* page.tpl.php (required).
* - #show_messages: Suppress drupal_get_message() items. Used by Batch
* API (optional).
*
* @see hook_page_alter()
* @see element_info()
*/
function drupal_render_page($page) {
$main_content_display = &drupal_static('system_main_content_added', FALSE);
// Allow menu callbacks to return strings or arbitrary arrays to render.
// If the array returned is not of #type page directly, we need to fill
// in the page with defaults.
if (is_string($page) || (is_array($page) && (!isset($page['#type']) || ($page['#type'] != 'page')))) {
drupal_set_page_content($page);
$page = element_info('page');
}
// Modules can add elements to $page as needed in hook_page_build().
foreach (module_implements('page_build') as $module) {
$function = $module . '_page_build';
$function($page);
}
// Modules alter the $page as needed. Blocks are populated into regions like
// 'sidebar_first', 'footer', etc.
drupal_alter('page', $page);
// If no module has taken care of the main content, add it to the page now.
// This allows the site to still be usable even if no modules that
// control page regions (for example, the Block module) are enabled.
if (!$main_content_display) {
$page['content']['system_main'] = drupal_set_page_content();
}
return drupal_render($page);
}
这个时候会组装$page这个数组，开始的时候，只包含节点部分，注意往下执行的时候，粗体部分的代码，定义了hook_page_build钩子函数，允许其它模块向$page数组追加内容。难道block模块实现了这个钩子函数？
