Drupal 9

Doc : https://www.drupal.org/docs/drupal-apis/form-api/conditional-form-fields

States that can be applied to a form field element:

Add following packages to composer.json file next to drupal repository

PHP Class using StringTranslationTrait

StringTranslationTrait allow to get t() and formatPlural() methods
Example:
use Drupal\Core\StringTranslation\StringTranslationTrait;
use Drupal\Core\StringTranslation\TranslationInterface;
class MyClass {


Import configuration file programmatically on Drupal 9 using config_update contrib module and service

//Update Module settings
\Drupal::service('config_update.config_update')->revert('system.simple', 'mymodule.settings');

State servic eallow to store variables such as state of the server temporarily or permanently

Examples:

Symptoms

You may have error messages like:

You can use IMCE to select a file.

This method allow to store data on drupal session using drupal session table (not php $_SESSION).
Storage is different for each users ans each visitors if anonymous

Install Redis

sudo apt-get update && sudo apt-get upgrade
sudo apt install redis-server
sudo apt install php-redis

Check

sudo systemctl status redis-server
redis-cli ping

Syntax:

\Drupal::service('page_cache_kill_switch')->trigger();

Example on a controller: