From Block API Overview:
Blocks in Drupal 8 are actually made up of two separate API structures to create a user experience similar to what Drupal has maintained in past iterations. These two APIs are the Block Plugin API, which is a stand-alone reusable API and the Block Entity API which is a Drupal 8 specific use case of block placement and visibility control.
Make sure you understand the Plugin API before continuing.
Steps for setting up a custom block:
- Create block plugin using annotations
- Extend the
Drupal\Core\Block\BlockBaseclass - Implement the necessary methods from the
Drupal\Core\Block\BlockPluginInterface
Example from Block API Overview:
use Drupal\Core\Block\BlockBase;
use Drupal\Core\Form\FormBuilderInterface;
use Drupal\Core\Form\FormStateInterface;
/**
* Provides a 'Fax' block.
*
* @Block(
* id = "fax_block",
* admin_label = @Translation("Fax block"),
* )
*/
class FaxBlock extends BlockBase {
// Access method here ...
/**
* {@inheritdoc}
*/
public function build() {
$config = $this->getConfiguration();
$fax_number = isset($config['fax_number']) ? $config['fax_number'] : '';
return array(
'#markup' => $this->t('The fax number is @number!', array('@number' => $fax_number)),
);
}
/**
* {@inheritdoc}
*/
public function blockForm($form, FormStateInterface $form_state) {
$form = parent::blockForm($form, $form_state);
// Retrieve existing configuration for this block.
$config = $this->getConfiguration();
// Add a form field to the existing block configuration form.
$form['fax_number'] = array(
'#type' => 'textfield',
'#title' => t('Fax number'),
'#default_value' => isset($config['fax_number']) ? $config['fax_number'] : '',
);
return $form;
}
/**
* {@inheritdoc}
*/
public function blockSubmit($form, FormStateInterface $form_state) {
// Save our custom settings when the form is submitted.
$this->setConfigurationValue('fax_number', $form_state->getValue('fax_number'));
}
/**
* {@inheritdoc}
*/
public function blockValidate($form, FormStateInterface $form_state) {
$fax_number = $form_state->getValue('fax_number');
if (!is_numeric($fax_number)) {
$form_state->setErrorByName('fax_block_settings', t('Needs to be an integer'));
}
}
}