How to have a reference to an extra factory

Question

I'm trying to have a reference to a model factory to load an object on desire. I just added a parameter to the constructor, but it generates an error:
(The parent constructor doesn't have the parameter: "\Magento\Catalog\Model\CategoryFactory $categoryFactory")

1 exception(s): Exception #0 (Exception): Recoverable Error: Argument 5 passed to Amaj\MegaMenu\Block\Html\Topmenu::__construct() must be an instance of Magento\Catalog\Model\CategoryFactory, none given, called in D:\ProgramFiles\wamp64\www\parastoo\var\generation\Amaj\MegaMenu\Block\Html\Topmenu\Interceptor.php on line 14 and defined in D:\ProgramFiles\wamp64\www\parastoo\app\code\Amaj\MegaMenu\Block\Html\Topmenu.php on line 33

What am I doing wrong? please help

Source code:

<?php

namespace Amaj\MegaMenu\Block\Html;

use Magento\Framework\DataObject\IdentityInterface;
use Magento\Framework\View\Element\Template;
use Magento\Framework\Data\TreeFactory;
use Magento\Framework\Data\Tree\Node;
use Magento\Framework\Data\Tree\NodeFactory;

/**
 * Html page top menu block
 */
class Topmenu extends \Magento\Theme\Block\Html\Topmenu
{

    protected $categoryFactory;


    /**
     * @param Template\Context $context
     * @param NodeFactory $nodeFactory
     * @param TreeFactory $treeFactory
     * @param array $data
     * @param \Magento\Catalog\Model\CategoryFactory $categoryFactory
     */
    public function __construct(
        Template\Context $context,
        NodeFactory $nodeFactory,
        TreeFactory $treeFactory,
        array $data = [],
        \Magento\Catalog\Model\CategoryFactory $categoryFactory
    ) {
        $this->categoryFactory = $categoryFactory;
        parent::__construct($context, $nodeFactory, $treeFactory, $data);
    }
}

Answer 1

When developing a module, we should care about generation files under var/generation. Sometimes, we meet:

Recoverable Error: Argument passed to __construct() must be an instance of

We should remove var/generation folder.