How to change the theme programmatically?

Question

I've just applied a theme and got an error such that I cannot even change the theme back to a working one (like Bartik).

I've read other threads but I could use hook_custom theme but I don't know how to get it to work.

What I'm doing is to edit the system.api.php and change the original lines of hook_custom_theme to this:

function hook_custom_theme() {
  // Allow the user to request a particular theme via a query parameter.
  if (1)) { 
    return 'bartik';
  }
}

I've tried several variations but I don't know what I'm missing. Can anyone help me with this please?

Edit: I've realised that I need to write my own module to run that line of code, is it true? Is there a simpler way to just change the default theme or the weight of the themes programmatically somewhere?

Answer 1

You can install drush on your system and then from drush command you can change the theme using

drush vset theme_default <theme_name>

You can do the changes from database also. Either on the commandline, or via an administration interface (eg PHPMyAdmin) enter the following query

UPDATE system SET status=1 WHERE name = '<theme_name>';

Then either:

UPDATE variable SET value='s:7:"garland"' WHERE name = 'theme_default';
TRUNCATE cache;
TRUNCATE cache_bootstrap;
TRUNCATE cache_block;

Source: https://drupal.org/node/200774