Why is my $node always null in my custom block (using plugin contexts)?

Question

I am trying to make a block that gets the current node via Plugin Contexts.

But my $node is always null. Can anyone tell me why?

I am placing the block with the context module if that makes a difference?

<?php

namespace Drupal\my_module\Plugin\Block;

use Drupal\Core\Block\BlockBase;

/**
 * Provides a 'Header' block.
 *
 * @Block(
 *   id = "header",
 *   admin_label = @Translation("Header"),
 *   context = {
 *     "node" = @ContextDefinition("entity:node", required = FALSE)
 *   }
 * )
 */
class ProductStickyHeader extends BlockBase {

  /**
   * {@inheritdoc}
   */
  public function build() {
    $build = [];

    $node = $this->getContextValue('node');
    // $node is always null!

    return $build;
  }
}

Many thanks!

Answer 1

Thanks everyone - turns out the answer was deceptively simple - I had to remove the block using context & then re-add it. When I re-added it there was an extra option in context to use the current node. Then the context plugin worked!

Answer 2

The most common way to get the current node in a block is to use the route parameters. E.g.:

$node = \Drupal::routeMatch()->getParameter('node');
if ( $node == NULL || $node->getType() != 'blog_post') {
  return;
}