Can't display as the final example from Chapter 4

[cuongdoan]

Hi John, recently I've just started to learn drupal. I read your book and followed your instruction in the book. However I was fail to display the as the final screenshot in your book. Even I just copied your zip file and still doesn't work. So Please guild me how to overcome this issue

[martinambrus]

10 years has passed and while learning Drupal basics on Drupal 7 today, I've encounered the same issue

solution is simple: clear all caches through the /admin/config/development/performance page - which is something the book author failed to mention

Drupal apparently doesn't only cache theme registry (which is remedied by enabling the Devel module and allowing it to rebuild it on every page load) but also hooks - which can only be cleared by the clear all caches button mentioned above