How can get category layered navigation using rest api in magento 2 for mobile api

Question

I'm creating rest api for mobile app in Magento 2,now i'm wondering to get layered navigation (filters) for a category and loaded collection like search or custom collection using rest api.

Please help

Answer 1

Have 2 mothod

Filter.php (api model)

    public function __construct(\Magento\Framework\Webapi\Rest\Request 
        $request){

                $this->_request         = $request;
        }


/**
     * Retrieve filterlist
     *
     * @api
     * @return array
     */
    public function retrieve(){     

        $category = $this->_request->getParam('categoryId');

        $objectManager = \Magento\Framework\App\ObjectManager::getInstance();

        $filterableAttributes = $objectManager->getInstance()->get(\Magento\Catalog\Model\Layer\Category\FilterableAttributeList::class);

        $appState = $objectManager->getInstance()->get(\Magento\Framework\App\State::class);
        $layerResolver = $objectManager->getInstance()->get(\Magento\Catalog\Model\Layer\Resolver::class);
        $filterList = $objectManager->getInstance()->create(
            \Magento\Catalog\Model\Layer\FilterList::class,
                [
                    'filterableAttributes' => $filterableAttributes
                ]
            );      

            $layer = $layerResolver->get();
            $layer->setCurrentCategory($category);
            $filters = $filterList->getFilters($layer);
            $maxPrice = $layer->getProductCollection()->getMaxPrice();
            $minPrice = $layer->getProductCollection()->getMinPrice();  

        $i = 0;
       foreach($filters as $filter)
       {
           //$availablefilter = $filter->getRequestVar(); //Gives the request param name such as 'cat' for Category, 'price' for Price
           $availablefilter = (string)$filter->getName(); //Gives Display Name of the filter such as Category,Price etc.
           $items = $filter->getItems(); //Gives all available filter options in that particular filter
           $filterValues = array();
           $j = 0;
           foreach($items as $item)
           {


               $filterValues[$j]['display'] = strip_tags($item->getLabel());
               $filterValues[$j]['value']   = $item->getValue();
               $filterValues[$j]['count']   = $item->getCount(); //Gives no. of products in each filter options
               $j++;
           }
           if(!empty($filterValues) && count($filterValues)>1)
           {
               $filterArray['availablefilter'][$availablefilter] =  $filterValues;
           }
           $i++;
       }  


        echo json_encode($filterArray);
        exit;

    }

Sample out put of this code will be:

{
    "availablefilter": {
        "Climate": [
            {
                "display": "All-Weather",
                "value": "202",
                "count": "1"
            },
            {
                "display": "Cool",
                "value": "204",
                "count": "1"
            }
        ],
        "Manufacturer": [
            {
                "display": "Azzedine Alaïa",
                "value": "216",
                "count": "1"
            },
            {
                "display": "Balenciaga",
                "value": "217",
                "count": "1"
            }
        ],
        "Material": [
            {
                "display": "Cotton",
                "value": "33",
                "count": "1"
            },
            {
                "display": "Nylon",
                "value": "37",
                "count": "1"
            }
        ],

Second method

public function __construct(
        \Magento\Catalog\Model\ResourceModel\Product\Attribute\CollectionFactory $productAttributeCollectionFactory
    ) {
        $this->productAttributeCollectionFactory = $productAttributeCollectionFactory;
    }

    public function getFilterableAttributes()
    {
        /** @var \Magento\Catalog\Model\ResourceModel\Product\Attribute\Collection $productAttributes */
        $productAttributes = $this->productAttributeCollectionFactory->create();
        $productAttributes->addFieldToFilter(
            ['is_filterable', 'is_filterable_in_search'],
            [[1, 2], 1]
        );

        return $productAttributes;
    }

Please refer this url : Magento 2 api - How to get layer navigation filters available in rest api?