newsupernova/app/code/Magefan/Blog/Observer/LayoutLoadBeforeObserver.php

<?php
/**
 * Copyright © 2015-2017 Ihor Vansach (ihor@magefan.com). All rights reserved.
 * See LICENSE.txt for license details (http://opensource.org/licenses/osl-3.0.php).
 *
 * Glory to Ukraine! Glory to the heroes!
 */

namespace Magefan\Blog\Observer;

use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\Data\Tree\Node;
use Magento\Store\Model\ScopeInterface;
use Magefan\Blog\Helper\Config;

/**
 * Disable page cache in preview mode
 */
class LayoutLoadBeforeObserver implements ObserverInterface
{

    /**
     * @var \Magento\Framework\Registry
     */
    protected $registry;

    /**
     * @param \Magento\Framework\Registry $registry
     */
    public function __construct(
        \Magento\Framework\Registry $registry
    ) {
        $this->registry = $registry;
    }

    /**
     * Page block html topmenu gethtml before
     *
     * @param \Magento\Framework\Event\Observer $observer
     * @return void
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     */
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        $post = $this->registry->registry('current_blog_post');
        if ($post && $post->getIsPreviewMode()) {
            $layout = $observer->getLayout();
            $layout->getUpdate()->addHandle('blog_non_cacheable');
        }
    }
}