1 ajax.inc ajax_base_page_theme()

Theme callback: Returns the correct theme for an Ajax request.

Many different pages can invoke an Ajax request to system/ajax or another generic Ajax path. It is almost always desired for an Ajax response to be rendered using the same theme as the base page, because most themes are built with the assumption that they control the entire page, so if the CSS for two themes are both loaded for a given page, they may conflict with each other. For example, Bartik is Backdrop's default theme, and Seven is the default administration theme. Depending on whether the "Use the administration theme when editing or creating content" checkbox is checked, the node edit form may be displayed in either theme, but the Ajax response to the Field module's "Add another" button should be rendered using the same theme as the rest of the page. Therefore, system_menu() sets the 'theme callback' for 'system/ajax' to this function, and it is recommended that modules implementing other generic Ajax paths do the same.

Return value

string|NULL: The name of the theme to be used, or NULL if the default should be used.

See also



Related topics


core/includes/ajax.inc, line 442
Functions for use with Backdrop's Ajax framework.


function ajax_base_page_theme() {
  if (!empty($_POST['ajax_page_state']['theme']) && !empty($_POST['ajax_page_state']['theme_token'])) {
    $theme = $_POST['ajax_page_state']['theme'];
    $token = $_POST['ajax_page_state']['theme_token'];

    // Prevent a request forgery from giving a person access to a theme they
    // shouldn't be otherwise allowed to see. However, since everyone is allowed
    // to see the default theme, token validation isn't required for that, and
    // bypassing it allows most use-cases to work even when accessed from the
    // page cache.
    if ($theme === config_get('system.core', 'theme_default') || backdrop_valid_token($token, $theme)) {
      return $theme;
  return NULL;