Drupal 8 stuff that's seemingly impossible to remember and FUN!

Drupal 8 Links

<?php

// Shamelessly borrowed from https://gist.github.com/r-daneelolivaw/b420b3dc0c40a6cacf76

// Autoload Url and Link classes.
use Drupal\Core\Url;
use Drupal\Core\Link;

/**
 * External link
 */
$url = Url::fromUri('https://colorfield.be');
$link = Link::fromTextAndUrl(t('Colorfield'), $url);
$link = $link->toRenderable();
$link['#attributes'] = array('class' => array('external'));
$output = render($link); 

/**
 * Internal route
 */
$url = Url::fromRoute('contact.site_page'); // a route provided in .routing.yml
$link = Link::fromTextAndUrl(t("Contact"), $url);
$link = $link->toRenderable();
$link['#attributes'] = array('class' => array('internal'));
$output = render($link);

/**
 * Entities, e.g. node
 * @see http://stackoverflow.com/questions/35397009/creating-a-link-from-node-id-in-drupal-8
 */
$options = ['absolute' => TRUE];
$url = Url::fromRoute('entity.node.canonical', ['node' => 1], $options);
//$url = $url->toString();
$link = Link::fromTextAndUrl("Node title", $url);
$link = $link->toRenderable();
$link['#attributes'] = array('class' => array('internal'));
$output = render($link);

/**
 * Internal path
 */
$path = '/my/path'; // prefixed with / 
$url = Url::fromUri('internal:'.$path);
$link = Link::fromTextAndUrl($label, $url);
$link = $link->toRenderable();
$link['#attributes'] = array('class' => array('internal'));
$output = render($link); 

/**
 * Anchor (current page)
 */
$url = Url::fromRoute('<current>', array(), array('fragment' => $name));
$link = Link::fromTextAndUrl($label, $url);
$link =  $link->toRenderable(); 
$output = render($link); 

Drupal 8 stuff that's seemingly impossible to remember and FUN!

Herein lies horrors of the likes that no one has ever encountered before. 
Take a deep breath and scroll down to reveal the code crapiness (or 1337ness) that will help one circumnavigate the open code ocean that is Drupal 8, 9, 10.. etc.

Output to dblog

<?php 
\Drupal::logger('your_lame_module')->notice('@type:  %title.',
        array(
            '@type' => "Massive Error",
            '%title' => "<pre>".print_r($error_array_or_text, true)."</pre>",
        ));

Redirect to a Page

<?php
use Symfony\Component\HttpFoundation\RedirectResponse;

$redirect = new RedirectResponse(Url::fromRoute('cat_module.route_name', ['route_arg' => 'a_value'])->toString());
$redirect->send();

Redirect to previous page after Login

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * @param $form
 * @param FormStateInterface $form_state
 * @param $form_id
 */
function MODULE_form_user_login_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  // Add another submit handler
  $form['#submit'][] = '_MODULE_user_login_form_submit';
}


/**
 * Redirect submit handler. We want the user to be redirected to the previous page after login
 *
 * @param $form
 * @param FormStateInterface $form_state
 */
function _MODULE_user_login_form_submit($form, FormStateInterface $form_state) {
  $previousUrl = \Drupal::requestStack()->getParentRequest()->getUri();
  $response = new TrustedRedirectResponse($previousUrl);
  $form_state->setResponse($response);
}

Setting arguments on Views blocks or pages (even AJAX)

/**
 * Implements hook_views_pre_view().
 */
function HOOK_views_pre_view(ViewExecutable $view, $display_id, array &$args) {
  if ($view->id() == 'view_id') {
    switch ($display_id) {
      case 'block_1':
        // Get exposed filters value
        $filter_input = $view->getExposedInput();
        // Field transfer data area.
        $filter_input['field_b'] = $filter_input['field_a'];
        $view->setExposedInput($filter_input);
        break;
    }
  }
}

States

State API is AWESOME because its super handy!

    Get a value:
    $val = \Drupal::state()->get('key');
     
    Get multiple key/value pairs:
    $pairs = \Drupal::state()->getMultiple($keys);
     
    Set a value:
    \Drupal::state()->set('key','value');
     
    Set multiple values:
    \Drupal::state()->setMultiple($keyvalues);
     
    Delete a value:
    \Drupal::state()->delete('key');