How do I use the global class \Drupal static methods to access services?

Question

Is there a difference between calling \Drupal::service('config.factory') and \Drupal::configFactory()?

Is it better to use the second one?

Can \Drupal be used to do something else than calling services?

The documentation says:

Accessing services in global functions

The global Drupal class provides static methods to access several of the most common services. For example, Drupal::moduleHandler() will return the module handler service or Drupal::translation() will return the string translation service. If there is no dedicated method for the service you want to use, you can use the Drupal::service() method to retrieve any defined service.

In which cases isn't there any dedicated method? How do I easily list all the retrievable services?

Answer 1

\Drupal::configFactory() is just shorter than \Drupal::service('config.factory'). The fact that with \Drupal::configFactory() you aren't hard-coding the service name in your module is not probably a reason to choose it, since you would still hard-code most of the service names (the dedicated methods don't even cover a quarter of all the available services), and the chances that a service name is changed are probably low now that Drupal 8 has a stable release.
When there is a dedicated method for a service I am using in my module, I much prefer using that dedicated method, and I prefer using dependency injection over using the static methods \Drupal has.

The purpose of the \Drupal class is giving access to the services provided from Drupal or third-party modules; even \Drupal::request() is calling a service's method. So, no, you don't use \Drupal for things that aren't services; even in this case, you should not depend from that class, if it is possible to use dependency injection.

For a list of the services implemented by modules, you need to look at the .services.yml files provided with the modules, including the core modules. Those files give you a list of services implemented by modules; it's impossible to give an exhaustive list since every module can implement all the services it needs.

Answer 2

\Drupal::service('config.factory') and \Drupal::configFactory() are equivalent; the second is just shorter.

There are many, many services provided by core, and only a few of them have a dedicated method. You can get a list of core services on the core.services.yml page. Note that this is not all services that core offers, for example, there are more services in user.services.yml.

Also note that when working with classes, it's better to use dependency injection rather than calling static methods. Static methods should be called in procedural code (in D8, this basically means hooks, or API functions).

This is a slideshow I used when doing a presentation on dependency injection at Drupal Camp Tokyo this month.