How to use custom class methods in the .theme preprocess functions?

Question

In a try to get code cleaner, I thought I could write a service in a custom module and use its methods within mytheme.theme, but obviously the preprocess functions signatures don't accept extra parameters.

In modules/custom/custom_module/src/Service/FooThemeHelpers.php

namespace Drupal\custom_module\Service;

class FooThemeHelpers 
{
  // Add a specific custom format 
  public function format_profile_adresse($field_profile_adresse){

    // do stuff ...

    return $markup;
  }
}

Then in mytheme.theme

use Drupal\custom_module\Service\FooThemeHelpers;

function mytheme_preprocess_views_view_fields(&$variables, FooThemeHelpers $themeHelpers) {

    if($variables['view']->id() == 'bar') {

      $markup = $themeHelpers->format_profile_adresse($variables['fields']['field_profile_adresse']->content);
      $variables['fields']['field_profile_adresse']->content = $markup;
  }
}

TypeError: Argument 2 passed to mytheme_preprocess_views_view_fields() must be an instance of Drupal\custom_module\Service\FooThemeHelpers, string given

I tried also with template_preprocess_page_title(), same error.

Should I declare and use static methods instead in my service ? Is there any Drupal coding standard way to export these helpers functions in a dedicated class, so that .theme remains lighter and readable... ?

Answer 1

The dependency injection coding standards only apply to most * classes.
In functions, use $service = \Drupal::service('service_name') to get the service.

To test code written in these functions, mock the services then build a custom container for them and assign it to Drupal using \Drupal::setContainer($container).

See Drupal\Tests\Core\Annotation\TranslationTest for an example of building a test container.

* Entity types, classes implementing TypedDataInterface, and certain plugins with custom plugin managers do not support dependency injection.

Answer 2

This is not exact answer to the question but to the code example there, so if you really trying to achieve the task in the example code, then the right way is to use custom FieldFormatter and you can set this one on any views and/or entity view_mode for field type address. You can easy get a boilerplate with drupal console command

drupal generate:plugin:fieldformatter

name it CustomAddressFieldFormatter for ex. This should happen in custom module. Pay attention to viewElements() method, address data is in $item, and you should return renderable array such as #markup, or any other valid,

  /**
   * {@inheritdoc}
   */
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];

    foreach ($items as $delta => $item) {
      //ksm($item);
      $elements[$delta] = ['#markup' => $item->getLocality()];
    }

    return $elements;
  }

or create your theme for an element and pass the data to it here. Above code will print the address City only for ex.

Look here https://www.drupal.org/docs/8/creating-custom-modules/creating-custom-field-types-widgets-and-formatters/create-a-custom-0 but instead in field_types Random you should use address

Then in views or entity viev_mode for field address, for Formatter you will have your custom formatter (Custom Address Field Formatter) as option to select - how this field to be rendered in the page.