1. Create a block call getProductCollection function.
    1. <?php
    3. /**
    4.  * Abm
    5.  *
    6.  * Author : Tony Liu
    7.  * Blog: https://www.abmbio.xin
    8.  *
    9.  * DISCLAIMER
    10.  *
    11.  * Do not edit or add to this file if you wish to upgrade this extension to newer
    12.  * version in the future.
    13.  *
    14.  * @package Tony_GetProductsByCategoryId
    15.  */
    17. namespace Tony\GetProductsByCategoryId\Block;
    19. class GetProducts extends \Magento\Framework\View\Element\Template
    20. {
    21.     protected $categoryFactory;
    23.     public function __construct(
    24.         \Magento\Framework\View\Element\Template\Context $context,
    25.         \Magento\Catalog\Model\CategoryFactory $categoryFactory
    26.     ) {
    27.         $this->categoryFactory = $categoryFactory;
    28.         parent::__construct($context);
    29.     }
    31.     public function getCategoryProduct($categoryId)
    32.     {
    33.         $category = $this->categoryFactory->create()->load($categoryId)->getProductCollection()->addAttributeToSelect('*');
    34.         return $category;
    35.     }
    36. }
    1. Show products in template.
    1. <?php
    3. /**
    4.  * @var $block \Tony\GetProductsByCategoryId\Block\GetProducts
    5.  */
    7. $categoryId = 5;
    8. $getProudctcollection = $block->getCategoryProduct($categoryId);
    10. ?>
    12. <ul class="category-products">
    13.     <?php foreach ($getProudctcollection as $product) : ?>
    14.         <li class="level0-child">
    15.             <a href="<?php echo $product->getProductUrl(); ?>">
    16.                 <?php echo $product->getName();?>
    17.             </a>
    18.         </li>
    19.     <?php endforeach;?>
    20. </ul>

    If done this, you will see products of one category.
    How to get products collection by category id in custom module - 图1

    If you need full package, please go my github.
    https://github.com/tonyabm/magento2-module-GetProductsByCategoryId