Magento 2 - Get checked checkbox values from grid on button click

Question

I have created a grid & have replaced "Add New" button action as below

    <?php
    namespace Company\Module\Block\Adminhtml;

    class Listproduct extends \Magento\Backend\Block\Widget\Grid\Container
    {
        public function __construct(
            \Magento\Backend\Block\Widget\Context $context,
            array $data = []
        ) {        
            parent::__construct($context, $data);
        }

       protected function _construct()
        {
            $urlData = $this->getRequest()->getParams();

            parent::_construct();
            $this->_controller = 'adminhtml_listproduct';
            $this->_blockGroup = 'Company_Module';
            $this->_headerText = __('Manage products');
            $this->_addButtonLabel = __('Save');
            $this->removeButton('add');
        }

        protected function _prepareLayout()
        {
            $this->buttonList->add(
                    'nameofbutton',
                    [
                        'label' => __('Add Selected Products'),
                        'onclick' => 'setLocation(\'' . $this->getUrl('*/listproduct/massaddproducts') . '\')',
                        'class' => 'add primary'
                    ],
                    0
            );
            return parent::_prepareLayout();
        }
    }

This is my grid.

My prepareColumn function from grid.php is

protected function _prepareColumns()
    {
        $this->addColumn(
            'id',
            [
                'header_css_class' => 'a-center',
                'type' => 'checkbox',
                'name' => 'id',
                'values' => $this->_getSelectedProducts(),
                'align' => 'center',
                'index' => 'entity_id',
                'use_index' => true
            ]
        );

        $this->addColumn(
            'entity_id',
            [
                'header' => __('entity_id'),
                'type' => 'number',
                'index' => 'entity_id',
                'header_css_class' => 'col-id',
                'column_css_class' => 'col-id'
            ]
        );
        $this->addColumn(
            'sku',
            [
                'header' => __('sku'),
                'index' => 'sku',
                'class' => 'sku'
            ]
        );

        $this->addColumn(
            'name',
            [
                'header' => __('name'),
                'index' => 'name',
                'class' => 'name'
            ]
        );        

        $block = $this->getLayout()->getBlock('grid.bottom.links');
        if ($block) {
            $this->setChild('grid.bottom.links', $block);
        }

        return parent::_prepareColumns();
    }

    protected function _getSelectedProducts()
    {
        return $this->getRequest()->getPost('selected', []);
    }

Controller is:-

    <?php
    namespace Company\Module\Controller\Adminhtml\Listproduct;

    class Massaddproducts extends \Magento\Backend\App\Action
    {
       protected $_productloader;  

       public function __construct(
            \Magento\Backend\App\Action\Context $context,
            \Magento\Catalog\Model\ProductFactory $_productloader
        ) {
            parent::__construct($context);
            $this->_productloader       = $_productloader;
        }

        public function execute()
        {
            $ids = $this->getRequest()->getParam('id');

            //$data = $this->getRequest()->getPost();
            $data = $this->getRequest()->getParams();

            echo '<pre>'; print_r($data); echo '</pre>'; exit;


        }
    }

I just want checked checkbox values on button click of "Add selected products"

Answer 1

Try the code shared below:-

class Massaddproducts extends \Magento\Backend\App\Action
{
   protected $_productloader;  
   protected $filter;

   public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Ui\Component\MassAction\Filter $filter, 
        \Magento\Catalog\Model\ProductFactory $_productloader
    ) {
        $this->filter = $filter;
        parent::__construct($context);
        $this->_productloader       = $_productloader;
    }

    public function execute()
    {
        $ids = $this->getRequest()->getParam('id');

        //$data = $this->getRequest()->getPost();
        $data = $this->getRequest()->getParams();
        $collection = $this->filter->
                      getCollection($this->_collectionFactory
                                ->create()
                                ); // get your selected collection

        $collectionSize = $collection->getSize();
        $items = $collection->getItems();

        foreach($items as $order){
            $postSelectedArr[] = $order->getId();
        }
        echo '<pre>';
        print_r($postSelectedArr);            

    }
}

I think you will have a better understanding form this thread:- Mass Action not sending all data

P.S:- If you get error for var/generation try deleting var/generation and try again