Force block page to use admin theme?

Question

I'm trying to use this snippet I found, but it throws this error:

function mytheme_init() {
  // Hardcode the administration theme onto the blocks page
  if ($_GET['q'] == 'admin/build/block') {
    global $theme;
    $theme = 'rubik';
  }
}

Fatal error: Unsupported operand types in /var/www/clients/client4/web39/web/modules/block/block.admin.inc on line 39

The $theme = 'rubik'; line appears to be the culprit in some way, as it doesn't throw the error if I comment it.

Answer 1

You have to use the global variable $custom_theme.
The implementation of your hook_init() is good.

Answer 2

There is a good module for this: Administration theme.

Drupal allows you to define a different theme for administration pages (Administer -> Site configuration -> Administration theme). By default this only applies to pages with a path starting with 'admin' and content editing pages.
The Administration theme module allows you to use this theme on more pages like:

• batch processing pages
• devel node load and render pages
• coder code review pages
• pages you define yourself in the provided textarea