How to change item custom option in cart

Question

I have products with custom options. One of these products options must be updated just after product has been added to cart.

I then created an event launched just after checkout_cart_add_product_complete.

My observer is well called :

public function execute(\Magento\Framework\Event\Observer $observer) {

    $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
    $cart = $objectManager->get('\Magento\Checkout\Model\Cart');
    $items = $cart->getQuote()->getAllItems();

    foreach ($items as $item)
    {
        $options = $item->getProduct()->getTypeInstance(true)->getOrderOptions($item->getProduct());
        $customOptions = $options['options'];
        if (!empty($customOptions)) 
        {
            foreach ($customOptions as $key=>$option) 
            {
                if ($option['label']=="foo") 
                {
                    $customOptions[$key]['value']="bar";
                }
            }

            $item->setProductOptions($customOptions);
            $item->save();
        }
    }
}

But when Cart is displayed, the product option has not been changed.

Thank you for your help,

Answer 1

        public function __construct(
                ...
                \Magento\Checkout\Model\Cart $cart
                ) 
        {
            ...
            $this->_cart=$cart;
        }

    public function execute(\Magento\Framework\Event\Observer $observer) {

        $items = $this->_cart->getquote()->getAllItems();

        foreach ($items as $item)
        {
            $options = $item->getProduct()->getTypeInstance(true)->getOrderOptions($item->getProduct());
            $customOptions = $options['options'];
            if (!empty($customOptions)) 
            {
                foreach ($customOptions as $key=>$option) 
                {
                    if ($option['label']=="foo") 
                    {
                        $OptionID=$option['option_id'];
                        $this->_cart->getquote()->getItemById($item->getItemId())->getOptionByCode('option_'.$OptionID)->setValue("bar");
                        break;
                    }
                }
                $buyreqTab=$this->serializer->unserialize($this->_cart->getquote()->getItemById($item->getItemId())->getOptionByCode('info_buyRequest')->getValue());
                $buyreqTab['options'][$OptionID]="bar";
                $this->_cart->getquote()->getItemById($item->getItemId())->getOptionByCode('info_buyRequest')->setValue($this->serializer->serialize($buyreqTab));
            }
            $this->_cart->save();

        }
    }

i tried it but it does not reflects in quote_item_options table