The Dependency injection (DI) means A class has dependency on another class B to provide some data or results, A class uses some methods of Class B to fulfill Business requirement.
Injection is process of Passing required dependency Parameter in constructor class or constructor method.
Magento 2.x or Adobe Commerce promotes dependency injection as a preferred approach for better code modularity, testability, reusability, and flexibility. Benefit of Dependency Injection
The following below two type Dependency Injection
1 – Magento 2 constructor injection
Constructor Injection is the preferred way to inject dependencies in Magento 2, as it addresses the most simple scenario where a class requires one or more dependency parameter
Constructor Injection To Pass or add a parameter in the class constructor to inject the dependency
<?php
namespace John\Mage2db\Block\Data;
class Data extends \Magento\Framework\View\Element\Template
{
protected $_customerSession;
protected $_viewHelper;
public function __construct(
\Magento\Framework\View\Element\Template\Context $context,
\Magento\Customer\Model\Session $customerSession,
\Magento\Customer\Helper\View $viewHelper
)
{
/* dependency injection of customerSession and viewHelper for Data class */
$this->_customerSession = $customerSession;
$this->_viewHelper = $viewHelper;
parent::__construct($context);
}
public function getCustomer()
{
return $this->_customerSession->getData(); // retrive customer data
}
public function getName()
{
/* To Get customer name with the help of viewHelper object's dependency */
/* injection using Customer data */
return $this->_viewHelper->getCustomerName($this->getCustomer());
}
}
?>Above code retrieve customer data by using customer session &
customer session (\Magento\Customer\Model\Session $customerSession) parameter passing inside constructor method
Magento 2 Method injection
Method Injection involves passing in a dependency as a method parameter to use it in the class logic.
When a particular method is dependent on class then we have to pass that class as dependency in our method, we should use Method Injection
<?php
namespace John\Mage2db\Observer;
use Magento\Framework\Event\ObserverInterface;
class OrderNumber implements ObserverInterface {
/**
* @param Magento\Framework\Event\Observer $observer
*/
public function execute(\Magento\Framework\Event\Observer $observer) {
$order = $observer->getEvent()->getOrder();
// Do Something Here
}
}
?>In the above Example, class parameter execute() retrieve Order Number by using Events / Observer & it completely depends on class
Magento\Framework\Event\Observer $observer
that’s why execute() passing class (Magento\Framework\Event\Observer $observer) as parameter to accomplish operation.