Make a Link list and Submenu
Example:
1. in yourmodule.links.menu.ymlyourmodule.test:
title: Test
parent: system.admin_config_development
route_name: yourmodule.test
Cache Clearing and rebuilding methods for Drupal 8
Site URL
1. Go to Administration > Configuration > Development > Performance
(/admin/config/development/performance)
2. Click on "Clear all caches"
Drush
drush cache-rebuild
OR
drush cr
Render Custom field with Drupal Renderer
Example 1, with FieldPluginBase (\Drupal\views\Plugin\views\field\FieldPluginBase)
JSON Encode and Decode
Example :
use Drupal\Component\Serialization\Json;
$json = Json::encode($data);
$data = Json::decode($json);