Magento 2: How to get sub category and their products in collection?

Question

I want to get the categories and related products in collection using parent category ID. So that i can show the grid like

sub category 1

sub category 1's product 1
sub category 1's product 2
sub category 1's product 3

sub category 2

sub category 2's product 1
sub category 2's product 2
sub category 2's product 3 

and so on. I can get the products in foreach but I need to add pagination also.

Answer 1

Step by step guide to add pagination in custom collection of Magento 2: 1 Create Collection for Pager:

protected $categorycollectionFactory;
    public function __construct(\Magecomp\Blog\Model\ResourceModel\Category\CollectionFactory $categorycollectionFactory) 
    { 
        $this->categorycollectionFactory = $categorycollectionFactory; 
    }
    public function getCategorydata()
    {
        $categoryId = 'yourcategoryid';
        $category = $this->_categoryFactory->create()->load($categoryId);
        $collection = $this->_productCollectionFactory->create();
        $collection->addAttributeToSelect('*');
        $collection->addCategoryFilter($category);
        $collection->addAttributeToFilter('visibility', \Magento\Catalog\Model\Product\Visibility::VISIBILITY_BOTH);
        $collection->addAttributeToFilter('status',\Magento\Catalog\Model\Product\Attribute\Source\Status::STATUS_ENABLED);
        return $collection;
    }

2. Add Collection to Pager and Set Available Limits.

   protected function _prepareLayout() { parent::_prepareLayout(); $this->pageConfig->getTitle()->set(__('Categories')); if ($this->getNews()) { $pager = $this->getLayout()->createBlock( 'Magento\Theme\Block\Html\Pager', 'magecomp.category.pager' )->setAvailableLimit(array(5=>5,10=>10,15=>15))->setShowPerPage(true)->setCollection( $this->getCategorydata() ); $this->setChild('pager', $pager); $this->getCategorydata()->load(); } return $this; }

3. Getting the Child Block of the Pager

   public function getPagerHtml() { return $this->getChildHtml('pager'); }

4. Add the following Code in phtml File to Call the Pager:

   <?php if ($block->getPagerHtml()): ?> <div class="order-products-toolbar toolbar bottom"><?php echo $block->getPagerHtml(); ?></div> <?php endif ?>