How To Get Current Derivative Block ID From Within hook_form_alter Function in Drupal 8?

Question

I'm building a custom Drupal 8 module which will make changes to a Webform based on the derivative plugin ID. I'm able to get the derivative plugin ID from within the build() function of the base block using $this->getDerivativeId() but It's not clear on how I can call getDerivativeId() from mycustommodule.module where I'm using hook_form_alter .

Any help would be greatly appreciated. Here is what I've tried so far without success:

1. I first tired $this->getDerivativeId() directly from hook_form_alter but I get an error

   "Using $this when not in object context"

2. Then I tried creating a new function in my base block class called "getCurrentBlockId()" where I would try to return the getDerivativeId() value but it forced me to make the function static and once I did that I could no longer use $this->getDerivativeId() .

    $block_id = \Drupal\transcode_profile\Plugin\Block\TranscodeBlockDerivative::getCurrentBlockId();

3. I also tried to creating a constructor to save the derivative block ID to a variable which would be accessible across the scope of my module but failed at that as well.

In summary, I can use $this->getDerivativId() at... \Drupal\transcode_profile\Plugin\Block\TranscodeBlockDerivative but need to use at... \Drupal\transcode_profile\transcode_profile.module and not sure how to do it.

Thanks in advance!

Answer 1

Not knowing much about your setup, but I believe you can achieve this by instantiating the plugin in question because you cannot call non-static methods statically and you can't use $this in non-object mode respectively.

Assuming you are after a block derivative you could try:

/* @var $manager \Drupal\Core\Block\BlockManagerInterface */
$manager = \Drupal::service('plugin.manager.block');

/* @var $block \Drupal\Core\Block\BlockPluginInterface */
$block = $manager->createInstance($block_id);

$derivative_id = $block->getDerivativeId();