<?php

namespace CustomConfirmControllerAdminhtmlOrder;

use MagentoFrameworkControllerResultFactory;
use MagentoBackendAppActionContext;
use MagentoUiComponentMassActionFilter;
use CustomConfirmModelResourceModelSaleslistCollectionFactory;

/**
 * Class Payseller.
 */
class MassConfirm extends MagentoBackendAppAction
{
     /**
     * @var MagentoSalesApiOrderRepositoryInterface
     */
    protected $_orderRepository;

    /**
     * @var MagentoSalesModelServiceInvoiceService
     */
    protected $_invoiceService;

    /**
     * @var MagentoFrameworkDBTransaction
     */
    protected $_transaction;

    protected $_order;

    public function __construct(
        MagentoFrameworkAppActionContext $context,
        MagentoSalesApiOrderRepositoryInterface $orderRepository,
        MagentoSalesModelServiceInvoiceService $invoiceService,
        MagentoSalesModelOrder $orderInfo,
        MagentoFrameworkDBTransaction $transaction
    ) {
        $this->_orderRepository = $orderRepository;
        $this->_order = $orderInfo;
        $this->_invoiceService = $invoiceService;
        $this->_transaction = $transaction;
        parent::__construct($context);
    }

    /**
     * Execute action.
     *
     * @return MagentoBackendModelViewResultRedirect
     *
     * @throws MagentoFrameworkExceptionLocalizedException|Exception
     */
    public function execute()
    {
            /** @var MagentoBackendModelViewResultRedirect $resultRedirect */
        $resultRedirect = $this->resultRedirectFactory->create();

        $wholedata = $this->getRequest()->getPost();

        foreach ($wholedata['selected'] as $orderId){


         $order = $this->_orderRepository->get($orderId);


                $order2=$this->_order->load($orderId);
                $items = $order2->getAllItems();
                echo $orderId;
                //var_dump($items);
                foreach($items as $i){
                 //var_dump($i);
                 // code to retrieve product id
                }


                  $objectManager = MagentoFrameworkAppObjectManager::getInstance();
                $order_ = $objectManager->create('MagentoSalesModelOrder')
                                           ->load($orderId);

                $order_->setState("processing")->setStatus("processing");

                $order_->save();

        }
        $this->messageManager->addSuccess(__('The order has been confirm. '));
        return $resultRedirect->setPath('sales/order/index');
    }

}

$order_ = $objectManager->create('MagentoSalesModelOrder')
                                       ->load($orderId);
$orderItems = $order_->getAllItems();
foreach ($orderItems as $item) {
        $proID = $item->getProductId();
        $itemSku = $item->getSku();
}

/**
 * @var MagentoCatalogModelProductFactory
 */
protected $_productFactory;



public function __construct(
    ...
    MagentoCatalogModelProductFactory $productFactory,
    ...
) {
    ...
    $this->_productFactory = $productFactory;
    ...
}

$order_ = $_objectManager->create('MagentoSalesModelOrder')
                                   ->load($orderId);
$orderItems = $order_->getAllItems();
foreach ($orderItems as $item)
{
    $productIds[] = $item->getProductId();

}

$collection = $this->_productFactory->create()->getCollection()->addAttributeToSelect(
        'name'
    )->addAttributeToSelect(
        'sku'
    )->addAttributeToSelect(
        'price'
    )->addAttributeToFilter(
        'entity_id', array('in' => $productIds)
    );