Drupal administration theme

Drupal允许为管理后台设置独立的theme，保存在系统变量variable_get('admin_theme')。

Drupal使用全局变量$theme来保存当前请求对应的主题。Drupal在启动时初始化$theme变量：

function _drupal_bootstrap_full() {
  ... ...
  menu_set_custom_theme();
  drupal_theme_initialize();
  module_invoke_all('init');
}

function menu_set_custom_theme() {
  menu_get_custom_theme(TRUE);
}

function menu_get_custom_theme($initialize = FALSE) {
  $custom_theme = &drupal_static(__FUNCTION__);
  // Skip this if the site is offline or being installed or updated, since the
  // menu system may not be correctly initialized then.
  if ($initialize && !_menu_site_is_offline(TRUE) && (!defined('MAINTENANCE_MODE') || (MAINTENANCE_MODE != 'update' && MAINTENANCE_MODE != 'install'))) {
    // First allow modules to dynamically set a custom theme for the current
    // page. Since we can only have one, the last module to return a valid
    // theme takes precedence.
    // 调用hook_custom_theme()获取自定义theme
    $custom_themes = array_filter(module_invoke_all('custom_theme'), 'drupal_theme_access');
    if (!empty($custom_themes)) {
      $custom_theme = array_pop($custom_themes);
    }
    // If there is a theme callback function for the current page, execute it.
    // If this returns a valid theme, it will override any theme that was set
    // by a hook_custom_theme() implementation above.
    // 在hook_menu()定义时也可以用theme callback/theme arguments定义theme
    $router_item = menu_get_item();
    if (!empty($router_item['access']) && !empty($router_item['theme_callback']) && function_exists($router_item['theme_callback'])) {
      $theme_name = call_user_func_array($router_item['theme_callback'], $router_item['theme_arguments']);
      if (drupal_theme_access($theme_name)) {
        $custom_theme = $theme_name;
      }
    }
  }
  return $custom_theme;
}

function drupal_theme_initialize() {
  global $theme, $user, $theme_key;

  // If $theme is already set, assume the others are set, too, and do nothing
  if (isset($theme)) {
    return;
  }

  drupal_bootstrap(DRUPAL_BOOTSTRAP_DATABASE);
  $themes = list_themes();

  // Only select the user selected theme if it is available in the
  // list of themes that can be accessed.
  // 检查有没有设置用户主题?
  $theme = !empty($user->theme) && drupal_theme_access($user->theme) ? $user->theme : variable_get('theme_default', 'bartik');

  // Allow modules to override the theme. Validation has already been performed
  // inside menu_get_custom_theme(), so we do not need to check it again here.
  // 检查有没有设置自定义主题？
  $custom_theme = menu_get_custom_theme();
  $theme = !empty($custom_theme) ? $custom_theme : $theme;

  ... ...
}

system模块实现了hook_custom_theme()钩子，检查当前请求menu是否属于admin：

function system_custom_theme() {
  if (user_access('view the administration theme') && path_is_admin(current_path())) {
    return variable_get('admin_theme');
  }
}

function path_is_admin($path) {
  $path_map = &drupal_static(__FUNCTION__);
  if (!isset($path_map['admin'][$path])) {
    $patterns = path_get_admin_paths();
    $path_map['admin'][$path] = drupal_match_path($path, $patterns['admin']);
    $path_map['non_admin'][$path] = drupal_match_path($path, $patterns['non_admin']);
  }
  return $path_map['admin'][$path] && !$path_map['non_admin'][$path];
}

system_custom_theme()调用path_is_admin()检查请求是否属于admin。path_is_admin()再调用path_get_admin_paths()返回哪些请求是admin，哪些请求是non_admin。

function path_get_admin_paths() {
  $patterns = &drupal_static(__FUNCTION__);
  if (!isset($patterns)) {
    $paths = module_invoke_all('admin_paths');
    drupal_alter('admin_paths', $paths);
    // Combine all admin paths into one array, and likewise for non-admin paths,
    // for easier handling.
    $patterns = array();
    $patterns['admin'] = array();
    $patterns['non_admin'] = array();
    foreach ($paths as $path => $enabled) {
      if ($enabled) {
        $patterns['admin'][] = $path;
      }
      else {
        $patterns['non_admin'][] = $path;
      }
    }
    $patterns['admin'] = implode("\n", $patterns['admin']);
    $patterns['non_admin'] = implode("\n", $patterns['non_admin']);
  }
  return $patterns;
}

path_get_admin_paths()如何判断请求是admin还是non_admin？这又要调用另外一个钩子hook_admin_paths()。system模块就实现了这个钩子：

function system_admin_paths() {
  $paths = array(
    'admin' => TRUE,
    'admin/*' => TRUE,
    'batch' => TRUE,
    // This page should not be treated as administrative since it outputs its
    // own content (outside of any administration theme).
    'admin/reports/status/php' => FALSE,
  );
  return $paths;
}

总结一下：
1. system模块通过实现hook_admin_paths()钩子定义了所有以admin/开头的请求都属于admin请求。
2. system模块通过实现hook_custom_theme()钩子定义了所有admin请求都使用admin_theme。