How can I inject data into a class using dependency injection XML?

Question

I'm under the impression that we can inject data into classes using di.xml and the $data array dependency. I'm struggling with getting it working however. Am I not understanding the concept correctly? Or am I missing some configuration?

Below is my (simplified) code.

etc/frontend/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="DannyNimmo\Subcategories\Block\ListCategory">
 <arguments>
 <argument xsi:type="array" name="data">
 <item xsi:type="string" name="test">test</item>
 </argument>
 </arguments>
 </type>
</config>

Block/ListCategory.php:

<?php
namespace DannyNimmo\Subcategories\Block;
class ListCategory
 extends \Magento\Framework\View\Element\Template
 implements \Magento\Framework\DataObject\IdentityInterface
{
 public function __construct (
 \Magento\Framework\View\Element\Template\Context $context,
 array $data = []
 ) {
 parent::__construct($context, $data);
 var_dump($data);
 }
}

Edit: I should say that I am seeing an empty array array(0) { } as the output.

• Andrew Noble: Have you tried re-running magento setup:di:compile or deleting the contents of the var/di and var/generation folders?
• Danny Nimmo: @AndrewNoble Yeah, I'm running in developer mode, and have cleared those directories multiple times.
• Kingshuk Deb: @DannyNimmo have you got the answer yet?

Answer 1

I can't test your code at the moment to solve your issue but I'd like to add something that can be useful.

DI is intended to pass injectables, that are classes that encapsulate some logic. DI shouldn't be used to pass data, the so called newables.

For example, if you need the data you are trying to inject, you should instead inject a class that is responsible of retrieving that data. This kind of classes are called repositories. In some circumstances it's better to use factories.

You can read more here.

Enjoy.

• Max: Are you sure? For example: there are multiple session managers. Each instance use custom session namespace ( like in Magento). Are you think, that we need to hardcode all namespaces in services ( SessionNamespaceProvider for example ) instead of setup namespaces values via di.xml?
• Danny Nimmo: In this case I was wanting to inject via DI for customisability, i.e. data can be easily added by another module. What is your opinion on the purpose of $data in this case?
• Max: @danny you can also set data values using layout configuration (attributes tag in block declaration)
• Alessandro Ronchi: Sorry @Max I don't understand your point. The di.xml is the "default" mapping between an interface declaration (the one you pass to the constructor) and the actual class you want to instantiate. It's ok to use di.xml to change that mapping for session managers that are a perfect example of injectables.
• Alessandro Ronchi: Hi @DannyNimmo I don't like the idea of passing data via di.xml; so said feel free to use the framework the way you prefer.