Magento 2 : Display cross sell products in products details page only for out of stock products:

Question

How to display cross sell products on the products details page for the out of stock products only?

Answer 1

Suppose, you want to add Crosssellsection at product detail page and want to show current product's Crosssellproducts then you need to create an extension.

On this extension, you will need to create a block which give you current product Crosssell products.

app/code/{VendorName}/{ModuleName}/Block/Crosssell.php

<?php
namespace {VendorName}\{ModuleName}\Block;

class Crosssell extends \Magento\Catalog\Block\Product\AbstractProduct
{
    /**
     * Crosssell item collection
     *
     * @var \Magento\Catalog\Model\ResourceModel\Product\Link\Product\Collection
     */
    protected $_itemCollection;

    /**
     * Prepare crosssell items data
     *
     * @return \Magento\Catalog\Block\Product\ProductList\Crosssell
     */
    protected function _prepareData()
    {
        $product = $this->_coreRegistry->registry('product');
        /* @var $product \Magento\Catalog\Model\Product */

        $this->_itemCollection = $product->getCrossSellProductCollection()->addAttributeToSelect(
            $this->_catalogConfig->getProductAttributes()
        )->setPositionOrder()->addStoreFilter();

        $this->_itemCollection->load();

        foreach ($this->_itemCollection as $product) {
            $product->setDoNotUseCategoryId(true);
        }

        return $this;
    }

    /**
     * Before rendering html process
     * Prepare items collection
     *
     * @return \Magento\Catalog\Block\Product\ProductList\Crosssell
     */
    protected function _beforeToHtml()
    {
        $this->_prepareData();
        return parent::_beforeToHtml();
    }

    /**
     * Retrieve crosssell items collection
     *
     * @return \Magento\Catalog\Model\ResourceModel\Product\Link\Product\Collection
     */
    public function getItems()
    {
        return $this->_itemCollection;
    }

    protected function _toHtml()
    {
            /* if product is out stock then render html  */
            if (!$this->_coreRegistry->registry('product')->isSaleable()) {
                return '';
            }
            return parent::_toHtml();
    }


}

Now, you need create layout file catalog_product_view.xml at

app/design/frontend/{Vendor}/{mytheme}/{VendorName}/{ModuleName}/layout

Now add below code at this layout files:

<?xml version="1.0"?>
<page layout="1column" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<referenceContainer name="content.aside">
    <block class="{VendorName}\{ModuleName}\Block\Product\ProductList\Crosssell" name="product.info.upsell" template="Magento_Catalog::product/list/items.phtml">
        <arguments>
            <argument name="type" xsi:type="string">upsell</argument>
        </arguments>
        <block class="Magento\Catalog\Block\Product\ProductList\Item\Container" name="crosssell.product.addto" as="addto">
            <block class="Magento\Catalog\Block\Product\ProductList\Item\AddTo\Compare"
                   name="upsell.product.addto.compare" as="compare"
                   template="Magento_Catalog::product/list/addto/compare.phtml"/>
        </block>
    </block>
 </referenceContainer>    
 </page>