Magento 2: Helper not working

Question

I am learning how to use dependency injections to get the classes I need.

The following will work when creating a controller.

...
use Magento\Framework\App\Action\Context;

class Index extends \Magento\Framework\App\Action\Action
{

  protected $_resultJsonFactory;
  protected $_directoryList;

  public function __construct(
    Context $context,
    \Magento\Framework\Controller\Result\JsonFactory $resultJsonFactory,
    \Magento\Framework\App\Filesystem\DirectoryList $directoryList
    )
  {
    $this->_resultJsonFactory = $resultJsonFactory;
    $this->_directoryList = $directoryList;
    parent::__construct($context);
  }
...

It can inject the dependencies I need. and I can then later use $this->_directoryList as needed.

I have tried to do the same for a helper class which needs access to this

...
class Data extends \Magento\Framework\App\Helper\AbstractHelper
{

  protected $_directoryList;

  public function __construct(
    \Magento\Framework\App\Filesystem\DirectoryList $directoryList,
    )
  {
    $this->_directoryList = $directoryList;
    parent::__construct();
  }
...

Whenever I add a constructor I start receiving 500 errors on any page that tries to call this helper.

Is there a proper method or way to inject dependencies into a helper class.

Answer 1

Create function getMediaPath() in helper and use this function in other files

class Data extends \Magento\Framework\App\Helper\AbstractHelper
{

    protected $_directoryList;

    public function __construct
    (
        \Magento\Framework\App\Helper\Context $context,
        \Magento\Framework\App\Filesystem\DirectoryList $directoryList
    ) {
        $this->_directoryList = $directoryList;
        parent::__construct($context);
    }

    public function getMediaPath()
    {
        return $this->directory_list->getPath('media');
    }
}

Answer 2

The issue error 500 was given by your helper constructor, where it calls parent::construct() without object.

Here parent is \Magento\Framework\App\Helper\AbstractHelper and its construct method needs \Magento\Framework\App\Helper\Context object.

So, to fix it just change your helper constructor to

public function __construct(
    \Magento\Framework\App\Helper\Context $context,
    \Magento\Framework\App\Filesystem\DirectoryList $directoryList
) {
    $this->_directoryList = $directoryList;
    parent::__construct($context);
}