How is the array $data parameter set in Magento 2 (dataObject constructor)

Question

In https://github.com/SnowdogApps/magento2-menu/blob/master/Block/Menu.php, a plugin that makes it possible to replace the default menu, the constructor of the block looks like below.

For all arguments / parameters in the constructor except array $data, my understanding is that those are somehow managed through the object manager and created if not existing. However, I'm stuck at figuring out how the array $data is set. In https://github.com/SnowdogApps/magento2-menu/blob/master/etc/di.xml, there is no argument named data.

Menu.php constructor:

public function __construct(
    Template\Context $context,
    EventManager $eventManager,
    MenuRepositoryInterface $menuRepository,
    NodeRepositoryInterface $nodeRepository,
    NodeTypeProvider $nodeTypeProvider,
    SearchCriteriaFactory $searchCriteriaFactory,
    FilterGroupBuilder $filterGroupBuilder,
    array $data = []
) {
    parent::__construct($context, $data);
    $this->menuRepository = $menuRepository;
    $this->nodeRepository = $nodeRepository;
    $this->nodeTypeProvider = $nodeTypeProvider;
    $this->searchCriteriaFactory = $searchCriteriaFactory;
    $this->filterGroupBuilder = $filterGroupBuilder;
    $this->eventManager = $eventManager;
}

I've looked on this related question (Magento 2: what is the $data array constructor parameter?) and went to myMagentoRootFolder/vendor/magento/framework/DataObject.php, to have a look on the class which is inherited and uses the $data-parameter, this didn't make me understand it. Furthermore, I don't that the default empty array would work, because the getData()-method is used by the module and an empty response would be of no use.

DataObject.php constructor:

/**
 * Constructor
 *
 * By default is looking for first argument as array and assigns it as object attributes
 * This behavior may change in child classes
 *
 * @param array $data
 */
public function __construct(array $data = [])
{
    $this->_data = $data;
}

*Menu.php extends Template, and Template extends AbstractBlock, and AbstractBlock extends DataObject

So, I don't understand how and where array $data is set. Any help is appreciated, as I've been struggling to understand this for some days.

Answer 1

Data is set when instantiating the object, either through factory(preferred) or through object manager.

Factory:

$this->factory->create(['data' => ['key' => 'value']]); 

Object Manager:

$this->_objectManager->create(\Class, ['data' => ['key' => 'value']]);

Data can be set after instantiating the object by using setData