Drupal 8 custom block (module) create twig template file

Question

I have a custom Module that creates a custom Block which has field elements.

This all works fine but I need to theme this block. I have checked the other posts on here

Answer 1

To be able to add the twig file in your module, you need to make sure the module defines the reference, not the theme.

You can still implement hook_theme() in the module's .module file as follows:

function mymodule_theme($existing, $type, $theme, $path) {
  return [
    'mymodule_block'     => [
      'variables' => [
        // define defaults for any variables you want in the twig file
        'attributes' => [
           'class' => ['my-module-class'],
         ], //etc
      ],
    ],
  ];
}

Then in your block's build() implementation you can add a reference to the new theme function:

public function build() {
    // Load the configuration from the form
    $config = $this->getConfiguration();
    $test_value = isset($config['test']) ? $config['test'] : '';

    $build = [];
    $build['#theme'] = 'mymodule_block';

    // You would not do both of these things...
    $build['#test_value'] = $test_value;
    $build['module_block_test']['#markup'] = '
' . $test_value . '
';

    return $build;
}

Finally be careful about where you place your twig file and what you name it. Create a templates directory in your module directory, and replace the _ in the theme function name with -: mymodule-block.html.twig