Dependency Injection in Drupal 8

What is Dependency Injection?

Injecting the dependency into your class

Types of Dependency Injection

• Constructor
  • Pass dependency as paramater of the __construct method of the class
  • Mandatory dependency
• Setter
  • Pass into a setter method in the class
  • Optional dependency
  • Cannot control dependency lifetime in the class
• Property
  • Similar to setter
  • Pass into a public property of the class.

Benefits

• Cleaner and modular code
• Reusable and flexible
• Abstracted
• Testable

DI in a Framework

Dependency injection == Dependency injection Container (DIC) == IOC Container == Service Container

What is a Service Container?

Creates a map of dependencies that classes need and handle loading/unloading

Symfony DI

• Services keys are strings e.g. ‘some_service’
• Service definitions specify which class to instantiate, the arguments to pass and additional methods to call on the object after instantiation
• Configure in PHP, XML or YAML
  • Can be ‘compiled’ down to PHP

Drupal 8 DI

2 ways to use core services:

• Service location: Used for procedural code e.g. Drupal::service('some_service')
• Service container: Used for OO code e.g. $container->get('some_service')

How and Where?

• Core services defined in core/core.services.yml
• Custom services defined in mymodule/mymodule.services.yml
• Custom classes live in mymodule/lib/Drupal/mymodule
• List of core services can be found at https://api.drupal.org/api/drupal/services