Magento – Dependency Injection and constructor parameters

best practicemagento2

Lets suppose I have extended a class from magento core and used some extra classes to have a specific functionality. Here is the code (just example).

// core code
public function __construct(
    \Magento\Framework\Model\Context $context,
    \Magento\Framework\Registry $registry,
    array $data = []
)

Now in my module I have added an extra class. Say it's catalog session. Now it looks like this

// module code
public function __construct(
    \Magento\Framework\Model\Context $context,
    \Magento\Framework\Registry $registry,
    \Magento\Catalog\Model\Session $catalogSession, //newly added
    array $data = []
)

Now I know Magento will go through all extended classes until it finds
out a constructor and those parameters will only use to inject
dependencies. So now here it will find the constructor in my module
first so it wont go to parent class at all and i need to ensure that I
will add all parameters from my parent class.

Now my question is what will happen if Magento will change or add or delete any parameters of its core class which we are extending?

Best Answer

Short answer: Your extension will crash.
Long answer:
If they change a constructor signature, the semantic version (major version) of the core module will be increased.
That's why you should declare dependencies in the composer.json file of your module and you should not use wildcards for the major version number of the dependencies.
This way you will get notified when trying to install your module that it will not work.

Related Solutions

Magento 2 – Add New Field to Magento_User Admin Form

For adding image field, you can try using plugin and always try to avoid overwrite whole class.

Vendor/Module/etc/adminhtml/di.xml


<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\User\Block\User\Edit\Tab\Main">
        <plugin name="sr_stackexchange_user_form" type="Vendor\Module\Plugin\Block\Adminhtml\User\Edit\Tab\Main" sortOrder="1"/>
    </type>
</config>

Vendor/Module/Plugin/Block/Adminhtml/User/Edit/Tab/Main.php


namespace Vendor\Module\Plugin\Block\Adminhtml\User\Edit\Tab;

class Main
{
    /**
     * Get form HTML
     *
     * @return string
     */
    public function aroundGetFormHtml(
        \Magento\User\Block\User\Edit\Tab\Main $subject,
        \Closure $proceed
    )
    {
        $form = $subject->getForm();
        if (is_object($form)) {
            $fieldset = $form->addFieldset('admin_user_image', ['legend' => __('User Image')]);
            $fieldset->addField(
                'user_image',
                'image',
                [
                    'name' => 'user_image',
                    'label' => __('Image'),
                    'id' => 'user_image',
                    'title' => __('Image'),
                    'required' => false,
                    'note' => 'Allow image type: jpg, jpeg, png'
                ]
            );

            $subject->setForm($form);
        }

        return $proceed();
    }
}

Clear cache.

Magento 2 – How to Define Constructor When Framework Class Gets Overwritten

You can use the Magento\Framework\Mail\MessageInterface interface in yours __construct method. If someone did rewrite of the class Magento\Framework\Mail\Message, then it shall implement this interface, but isn't obliged to extend a base class.

// Vendor\Module\Helper\Debug
public function __construct(
    \Magento\Framework\App\Helper\Context $context,
    \Magento\Framework\Mail\MessageInterface $message,
    \Magento\Framework\Mail\TransportInterface $transport,
    \Vendor\Module\Helper\Config $configHelper
) {
    ...
    parent::__construct($context);
}

You can read more info here I think third-party module developers make a low-quality rewrite and they don't think about how their module will works with another modules. In my opinion they should extend base class in their rewrite-class.

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