Magento 2: Add a product to the cart programmatically

Question

I am quite new to Magento and have the requirement to add a predetermined free product to the shopping cart each time the customer adds something else. So far I have added an observer to watch for the 'checkout_cart_product_add_after' event.

I have used the following code in my observer but when I add a product to the cart, a message is displayed saying

"We can't add this product to the basket right now"

use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\App\RequestInterface;
use Magento\Framework\View\Result\PageFactory;

class AddProduct implements ObserverInterface
{
    protected $resultPageFactory;
    protected $_productRepository;
    protected $_cart;
    protected $formKey;

    public function __construct(
        \Magento\Catalog\Model\ProductRepository $productRepository,
        \Magento\Checkout\Model\Cart $cart,
        \Magento\Framework\Data\Form\FormKey $formKey,
        PageFactory $resultPageFactory
    )
    {
        $this->resultPageFactory = $resultPageFactory;
        $this->_productRepository = $productRepository;
        $this->_cart = $cart;
        $this->formKey = $formKey;
    }

    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        $productId =10;

        $params = array(
            'form_key' => $this->formKey->getFormKey(),
            'product' => $productId, //product Id
            'qty'   =>1 //quantity of product
        );
        //Load the product based on productID
        $_product = $this->product->load($productId);
        $this->cart->addProduct($_product, $params);
        $this->cart->save();

    }

}

I hope somebody is able to explain what is going wrong here or point me in a different direction if this approach will not work. I am using version 2.2 of Magento.

Many thanks

Answer 1

protected $formKey;   
protected $cart;
protected $product;

public function __construct(
\Magento\Framework\App\Action\Context $context,
\Magento\Framework\Data\Form\FormKey $formKey,
\Magento\Checkout\Model\Cart $cart,
\Magento\Catalog\Model\Product $product,
array $data = []) {
    $this->formKey = $formKey;
    $this->cart = $cart;
    $this->product = $product;      
    parent::__construct($context);
}

public function execute()
 { 
  $productId =10;
  $params = array(
                'form_key' => $this->formKey->getFormKey(),
                'product' => $productId, //product Id
                'qty'   =>1 //quantity of product                
            );              
    //Load the product based on productID   
    $_product = $this->product->load($productId);       
    $this->cart->addProduct($_product, $params);
    $this->cart->save();
 }

Answer 2

according to the docblock of Magento\Quote\Model\Quote::AddProduct(), $params should have to convert into \Magento\Framework\DataObject

<?php
namespace Vendor\Extension\Controller\Index;

use Magento\Catalog\Model\Product;
use Magento\Catalog\Model\ProductRepository;
use Magento\Checkout\Model\Session;
use Magento\Framework\App\Action\Action;
use Magento\Framework\App\Action\Context;
use Magento\Framework\Data\Form\FormKey;
use Magento\Framework\DataObject\Factory;
use Magento\Framework\Exception\CouldNotSaveException;
use Magento\Framework\Exception\LocalizedException;
use Magento\Framework\Exception\NoSuchEntityException;
use Magento\Quote\Api\CartRepositoryInterface;

class Post extends Action
{
    protected $formKey;
    private $checkoutSession;
    private $productRepository;
    private $dataObjectFactory;
    private $cartRepository;

    public function __construct(
        Context $context,
        FormKey $formKey,
        Session $checkoutSession,
        ProductRepository $productRepository,
        Factory $dataObjectFactory,
        CartRepositoryInterface $cartRepository
    ) {
        $this->formKey = $formKey;
        $this->checkoutSession = $checkoutSession;
        $this->productRepository = $productRepository;
        $this->dataObjectFactory = $dataObjectFactory;
        $this->cartRepository = $cartRepository;
        parent::__construct($context);
    }
    public function execute()
    {
        $productId =10;
        $params = [
            'form_key' => $this->formKey->getFormKey(),
            'product' => $productId,
            'qty'   =>1
        ];
        try {
            $product = $this->productRepository->getById($productId);
            $cart = $this->checkoutSession->getQuote();
            $cart->addProduct(
                $product,
                $this->dataObjectFactory->create($params)
            );
            $this->cartRepository->save($cart);
        } catch (NoSuchEntityException $e) {
            //@todo no product with given ID
        } catch (LocalizedException $e) {
            //@todo error during addProduct or local during saving cart
        } catch (CouldNotSaveException $e) {
            //@todo unable to save cart
        } catch (\Exception $e) {
            //@todo there could be more type of exceptions than stated above
        }
    }
}

also:

• use repository if possible
• get cart from checkout session

Answer 3

try below code

<?php
    namespace Vendor\Extension\Controller\Index;
    use Magento\Framework\App\Action\Action;
    use Magento\Framework\App\Action\Context;
    use Magento\Framework\Data\Form\FormKey;
    use Magento\Checkout\Model\Cart;
    use Magento\Catalog\Model\Product;
    class Post extends Action
    {
        protected $formKey;   
        protected $cart;
        protected $product;
        public function __construct(
            Context $context,
            FormKey $formKey,
            Cart $cart,
            Product $product) {
                $this->formKey = $formKey;
                $this->cart = $cart;
                $this->product = $product;      
                parent::__construct($context);
        }
        public function execute()
         { 
            $productId =10;
            $params = array(
                        'form_key' => $this->formKey->getFormKey(),
                        'product' => $productId, 
                        'qty'   =>1
                    );              
            $product = $this->product->load($productId);       
            $this->cart->addProduct($product, $params);
            $this->cart->save();
         }
    }