Magento – How to add custom button to grid ui

By default Magento2 not include js for dropdown.So override and use product_listing.xml in your module and add your column class for category options.( for format : see status)

Path:

<vendor>/<module>view/adminhtml/ui_component/product/product_listing.xml

and use below code :-

<?xml version="1.0" encoding="UTF-8"?>
<listing xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
  <listingToolbar name="listing_top">     
    <filters name="listing_filters">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="templates" xsi:type="array">
                        <item name="filters" xsi:type="array">
                            <item name="select" xsi:type="array">
                                <item name="component" xsi:type="string">Magento_Ui/js/form/element/ui-select</item>
                                <item name="template" xsi:type="string">ui/grid/filters/elements/ui-select</item>
                            </item>
                        </item>
                    </item>
                </item>
            </argument>
    </filters>
</listingToolbar>
    <columns name="product_columns" class="Magento\Catalog\Ui\Component\Listing\Columns">
        <column name="category_ids" class="<VENDOR><MODULE_NAME>\Ui\Component\Listing\Column\Category">
            <argument name="data" xsi:type="array">
               <item name="options" xsi:type="object"><VENDOR><MODULE_NAME>\Model\Category\Categorylist</item>
                <item name="config" xsi:type="array">
                   <item name="filter" xsi:type="string">select</item>
                    <item name="add_field" xsi:type="boolean">true</item>
                    <item name="dataType" xsi:type="string">select</item>
                    <item name="label" xsi:type="string" translate="true">Categories</item>
                    <item name="sortOrder" xsi:type="number">100</item>
                </item>
            </argument>
        </column>
     </columns>
</listing>

Use button like here

And then add following line inside buttons tag

<button name="custom_button_name" class="Vendor\Module\Block\Adminhtml\CustomButton"/>

Vendor/Module/Block/Adminhtml/CustomButton.php

namespace Vendor\Module\Block\Adminhtml;

use Magento\Framework\View\Element\UiComponent\Control\ButtonProviderInterface;

class CustomButton implements ButtonProviderInterface
{
    /**
     * Url Builder
     *
     * @var \Magento\Framework\UrlInterface
     */
    protected $urlBuilder;

    /**
     * CustomButton constructor.
     *
     * @param \Magento\Backend\Block\Widget\Context $context
     */
    public function __construct(
        \Magento\Backend\Block\Widget\Context $context
    ) {
        $this->urlBuilder = $context->getUrlBuilder();
    }
    /**
     * @return array
     */
    public function getButtonData()
    {
        $data = [
            'label' => __('Custom Button'),
            'class' => 'save primary',
            'id' => 'custom-button',
            'on_click' => sprintf("location.href = '%s';", $this->getUrl('*/*/url', ['id' => 2])),
            'sort_order' => 20,
        ];
        return $data;
    }

    /**
     * Generate url by route and parameters
     *
     * @param   string $route
     * @param   array $params
     * @return  string
     */
    public function getUrl($route = '', $params = [])
    {
        return $this->urlBuilder->getUrl($route, $params);
    }
}