Error message not displaying in Observer Magento2

Question

I used below event,

<event name="catalog_controller_product_view">
    <observer name="custom_product_view_layout" instance="Vendor\Module\Observer\CheckProduct" />
</event>

Then in my observer file,

namespace Vendor\Module\Observer;

use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\Event\Observer;

class CheckProduct implements ObserverInterface 
{
  protected $_logger;
  protected $_storeManager;
  protected $messageManager;
  protected $productRepository;
  protected $_resultPageFactory;

 public function __construct(
    \Psr\Log\LoggerInterface $logger,       
    \Magento\Store\Model\StoreManagerInterface $storeManager,
    \Magento\Framework\Message\ManagerInterface $messageManager,
    \Magento\Catalog\Api\ProductRepositoryInterface $productRepository,
    \Magento\Framework\View\Result\PageFactory $resultPageFactory
) {
    $this->_logger = $logger;
    $this->_storeManager  = $storeManager;
    $this->messageManager = $messageManager;
    $this->_resultPageFactory = $resultPageFactory;
    $this->productRepository = $productRepository;
}

public function execute(Observer $observer) {
    $product = $observer->getEvent()->getProduct();     
    if($this->_ciicustomerHelper->isCustomerLoggedIn()) {   
        try{
            //Exam Service Api data
            $productSku = $product->getSku();
            $source_sku = $this->checkProduct($productSku);
            if(isset($source_sku) && $source_sku != false) :
                $message = "You can not buy this product";
                $this->messageManager->addError(__($message));  
            endif;              
          } catch (\Exception $ex) {
                $this->_logger->info("Message ".$ex->getMessage());
          }
    }
    return $this;
 } 
 public function checkProduct($productSku){
    $connection = $this->getConnection();
   $sql = "select * from custom_table where sku='".$productSku."'";
   $resultProduct = $connection->query($sql);
   $resultQuery = $resultProduct->fetchAll();

  if(!empty($resultQuery)){ 
    $parent_sku = $resultQuery[0]['parent_sku'];
    return true;
   }
  }else{
   return false;
  }
  }

}

This is not displaying any error message, can anyone help me on this please what is wrong in the code.

Thanks

Answer 1

You have the syntax issue.

class CheckProduct implements ObserverInterface {

    protected $_logger;
    protected $_storeManager;
    protected $messageManager;
    protected $productRepository;
    protected $_resultPageFactory;

    public function __construct(
            \Psr\Log\LoggerInterface $logger,
            \Magento\Store\Model\StoreManagerInterface $storeManager,
            \Magento\Framework\Message\ManagerInterface $messageManager,
            \Magento\Catalog\Api\ProductRepositoryInterface $productRepository,
            \Magento\Framework\View\Result\PageFactory $resultPageFactory
    ) {
        $this->_logger = $logger;
        $this->_storeManager = $storeManager;
        $this->messageManager = $messageManager;
        $this->_resultPageFactory = $resultPageFactory;
        $this->productRepository = $productRepository;
    }

    public function execute(Observer $observer) {
        $product = $observer->getEvent()->getProduct();
        if ($this->_ciicustomerHelper->isCustomerLoggedIn()) {
            try {
                //Exam Service Api data
                $productSku = $product->getSku();
                $source_sku = $this->checkProduct($productSku);
                if (isset($source_sku) && $source_sku != false) :
                    $message = "You can not buy this product";
                    $this->messageManager->addError(__($message));
            //} //synxtax issue
            endif;
        } catch (\Exception $ex) {
            $this->_logger->info("Message " . $ex->getMessage());
        }
    }
    return $this;
}

public function checkProduct($productSku) {
    $connection = $this->getConnection();
    $sql = "select * from custom_table where sku='" . $productSku . "'";
    $resultProduct = $connection->query($sql);
    $resultQuery = $resultProduct->fetchAll();

    if (!empty($resultQuery)) {
        $parent_sku = $resultQuery[0]['parent_sku'];
        return true;
   // } //synxtax issue
    } else {
        return false;
    }
}

Also, the event is not right, you can use event catalog_controller_product_init_after

    $this->_eventManager->dispatch(
        'catalog_controller_product_init_after',
        ['product' => $product, 'controller_action' => $controller]
    );

You donot need to add \Magento\Framework\View\Result\PageFactory $resultPageFactory,remove it from __construct

Modified Code:

 <?php

namespace Vendor\Module\Observer;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;

class CheckProduct implements ObserverInterface
{
    private $_logger;
    private $_storeManager;
    private $messageManager;

    public function __construct(
        \Psr\Log\LoggerInterface $logger,
        \Magento\Store\Model\StoreManagerInterface $storeManager,
        \Magento\Framework\Message\ManagerInterface $messageManager
    ) {
        $this->_logger = $logger;
        $this->_storeManager = $storeManager;
        $this->messageManager = $messageManager;
    }

    public function execute(Observer $observer)
    {
        $product = $observer->getEvent()->getProduct();

        try {
            $source_sku = $this->checkProduct($product->getSku());
            if ($source_sku) {
                $message = "You can not buy this product";
                $this->messageManager->addErrorMessage(__($message));
            }
        } catch (\Exception $ex) {
            $this->_logger->info("Message " . $ex->getMessage());
        }

        return $this;
    }

    public function checkProduct($productSku)
    {
        return true;
        $connection = $this->getConnection();
        $sql = "select * from custom_table where sku='" . $productSku . "'";
        $resultProduct = $connection->query($sql);
        $resultQuery = $resultProduct->fetchAll();

        if (!empty($resultQuery)) {
            $parent_sku = $resultQuery[0]['parent_sku'];
            return true;
        } else {
            return false;
        }
    }
}