How do I inject a dateFormatter servide into a service class named MyService?

Question

I have a service class declared like this:

 class MyService implements MyServiceInterface {

I want to get rid of a (working) call to a the static \Drupal::service('date.formatter') function and replace with a injected call to $this->dateFormatter.

I am looking at the most upvoted answer to this question: Make a custom date formatter for view.

It suggests that you can output a custom formatted timestamp like this:

$now = \Drupal::time()->getCurrentTime();
$currenttime = $this->dateFormatter->format($now, 'custom', 'Y-m-d H:i');

However, this does not work for me. It uses an injected call to the public function DateFormatter::format, and the upvoted answer does not explain how to set up the class where it is used to inject this service. This produces a WSOD on my site. The cause is obviously that dateFormatter has not been initialized.

As noted, I know that using a static call works:

$now = \Drupal::time()->getCurrentTime();
$currenttime = \Drupal::service('date.formatter')->format($now, 'custom', 'Y-m-d H:i');

I have a rough idea bout how to set up a service class to initialize an injected service. I.e. I think to be able to use it, I need to do at least three things:

1. Declare the injected service as an argument in myservice.services.yml.
2. Declare the injected property as a $protected variable.
3. Initialize it in the class' contructor.

But I am not even sure if this is correct. And the details eludes me. For example: How do I discover what name to include in myservice.services.yml?

Any guidance will be appreciated.

PS: I have studied this answer: How do I inject services in a service, but I don't understand how it applies to my question.

It has been suggested that Inject a class as dependecy injection in a service is a duplicate. The accepted answer to that question is not about the @date.formatter service that is the subject of my question, and it does not mention using autowire to solve the problem. (Which I learned how to use in the answer I now have accepted.)

Answer 1

But I am not even sure if this is correct. And the details eludes me. For example: How do I discover what name to include in myservice.services.yml?

Now that Drupal 9 is end of life you no longer need to do that. Replace the argument list with the autowire option:

mymodule.services.yml

services:
  mymodule.my_service:
    class: Drupal\mymodule\MyService
    autowire: true

and in the service class:

  /**
   * The date formatter.
   *
   * @var \Drupal\Core\Datetime\DateFormatterInterface
   */
  protected $dateFormatter;

  /**
   * Constructs \Drupal\mymodule\MyService
   *
   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
   *   The date formatter.
   */
  public function __construct(DateFormatterInterface $date_formatter) {
    $this->dateFormatter = $date_formatter;
  }

So to discover the service you only need the interface DateFormatterInterface. Use autocomplete and the IDE will automatically add a use statement at the top:

use Drupal\Core\Datetime\DateFormatterInterface;

See the change record: Core services provide aliases for autowiring