Difference when to declare an object via Magento\Framework\ObjectManagerInterface and inject via the constructor

Question

I'm initializing an object \Magento\Framework\Registry via a function create() of Magento\Framework\ObjectManagerInterface in Controller. After, I try to register a value to Registry Class.

$registry = $this->_objectManager->create('Magento\Framework\Registry');
$registry->register('test', '123456');

I try to get this value in Block. However, it return null.

$registry->registry('test'); //return null

If I inject \Magento\Framework\Registry to the constructor, it working normally.

public function __construct(
    Magento\Framework\App\Action\Context $context,
    \Magento\Framework\Registry $registry
) {
    parent::__construct($context);
    $this->registry = $registry;
}

My question: Why this two ways different initialization?

Any help is appreciated.

Answer 1

why are we using get() neither create() ?

Create always Create new object instance

Ref

public function create($type, array $arguments = [])
{
    $type = ltrim($type, '\\');
    return $this->_factory->create($this->_config->getPreference($type), $arguments);
}

Get retrieve existing object instance(if find any)

public function get($type)
{
    $type = ltrim($type, '\\');
    $type = $this->_config->getPreference($type);
    if (!isset($this->_sharedInstances[$type])) {
        $this->_sharedInstances[$type] = $this->_factory->create($type);
    }
    return $this->_sharedInstances[$type];
}

For more information please check

\vendor\magento\framework\ObjectManager\ObjectManager.php

Hope it helps.

Answer 2

You need to define registry using get() method and its working same as constructor,

$registry = $this->_objectManager->get('Magento\Framework\Registry')->register('test', '123456');

and getting registry value using below method,

$this->_objectManager->get('Magento\Framework\Registry')->registry('test');