Magento 2 add column to sales returns grid

Question

How to add column to sales returns grid, returns grid using _prepareColumns to add columns to grid \Magento\Rma\Block\Adminhtml\Rma\Grid

Answer 1

Try with below way!

Extend Magento RMA block file to your custom module.

app/code/Namespace/Modulename/Block/Adminhtml/Rma

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

// @codingStandardsIgnoreFile

namespace Namespace\Modulename\Block\Adminhtml\Rma;

/**
 * RMA Grid
 */
class Grid extends \Magento\Rma\Block\Adminhtml\Rma\Grid
{
    /**
     * @param \Magento\Backend\Block\Template\Context $context
     * @param \Magento\Backend\Helper\Data $backendHelper
     * @param \Magento\Rma\Model\ResourceModel\Rma\Grid\CollectionFactory $collectionFactory
     * @param \Magento\Rma\Model\RmaFactory $rmaFactory
     * @param array $data
     */
    public function __construct(
        \Magento\Backend\Block\Template\Context $context,
        \Magento\Backend\Helper\Data $backendHelper,
        \Magento\Rma\Model\ResourceModel\Rma\Grid\CollectionFactory $collectionFactory,
        \Magento\Rma\Model\RmaFactory $rmaFactory,
        array $data = array())
    {
        parent::__construct(
            $context,
            $backendHelper,
            $collectionFactory,
            $rmaFactory,
            $data);
    }

    /**
     * Prepare related item collection
     *
     * @return \Magento\Rma\Block\Adminhtml\Rma\Grid
     */
    protected function _prepareCollection()
    {
        $this->_beforePrepareCollection();
        return parent::_prepareCollection();
    }

    /**
     * Configuring and setting collection
     *
     * @return $this
     */
    protected function _beforePrepareCollection()
    {
        if (!$this->getCollection()) {
            /** @var $collection \Magento\Rma\Model\ResourceModel\Rma\Grid\Collection */
            $collection = $this->_collectionFactory->create();
            $this->setCollection($collection);
        }
        return $this;
    }

    /**
     * Prepare grid columns
     *
     * @return \Magento\Rma\Block\Adminhtml\Rma\Grid
     */
    protected function _prepareColumns()
    {
        parent::_prepareColumns();
        $this->addColumn(
            'custom_column',
            [
                'header' => __('Custom Column'),
                'index' => 'custom_column',
                'header_css_class' => 'col-name',
                'column_css_class' => 'col-name'
            ]
        );
        return $this;
    }

    /**
     * Prepare massaction
     *
     * @return $this
     */
    protected function _prepareMassaction()
    {
        $this->setMassactionIdField('entity_id');
        $this->getMassactionBlock()->setFormFieldName('entity_ids');

        $this->getMassactionBlock()->addItem(
            'status',
            [
                'label' => __('Close'),
                'url' => $this->getUrl($this->_getControllerUrl('close')),
                'confirm' => __(
                    'You have chosen to change status(es) of the selected RMA requests to Close.'
                    . ' Are you sure you want to continue?'
                )
            ]
        );

        return $this;
    }

    /**
     * Get Url to action
     *
     * @param  string $action action Url part
     * @return string
     */
    protected function _getControllerUrl($action = '')
    {
        return '*/*/' . $action;
    }

    /**
     * Retrieve row url
     *
     * @param \Magento\Framework\DataObject $row
     * @return string
     */
    public function getRowUrl($row)
    {
        return $this->getUrl($this->_getControllerUrl('edit'), ['id' => $row->getId()]);
    }
}

It will be showing like below.

I hope it helps!

Answer 2

Step 1 : 
    Create Custom Column (Token Number) In Rma Grid Table

Step 2:
    Use preference in di.xml 
    "<preference for="Magento\Rma\Block\Adminhtml\Rma\Grid" type="<Vendor>\<ModuleName>\Block\Adminhtml\Rma\Grid" />"

Step 3:

    Create Grid Class   <Vendor>\<ModuleName>\Block\Adminhtml\Rma\Grid 

<?php

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

namespace <Vendor>\<ModuleName>\Block\Adminhtml\Rma;

/**
 * Description of Grid
 *
 * @author sagar
 */
class Grid extends \Magento\Rma\Block\Adminhtml\Rma\Grid {


    /**
     * @param \Magento\Backend\Block\Template\Context $context
     * @param \Magento\Backend\Helper\Data $backendHelper
     * @param \Magento\Rma\Model\ResourceModel\Rma\Grid\CollectionFactory $collectionFactory
     * @param \Magento\Rma\Model\RmaFactory $rmaFactory
     * @param array $data
     */
    public function __construct(
            \Magento\Backend\Block\Template\Context $context,
            \Magento\Backend\Helper\Data $backendHelper,
            \Magento\Rma\Model\ResourceModel\Rma\Grid\CollectionFactory $collectionFactory,
            \Magento\Rma\Model\RmaFactory $rmaFactory,
            array $data = array()) {
        parent::__construct(
                $context,
                $backendHelper,
                $collectionFactory,
                $rmaFactory,
                $data);
    }

    /**
     * Prepare related item collection
     *
     * @return \Magento\Rma\Block\Adminhtml\Rma\Grid
     */
    protected function _prepareCollection() {
        $this->_beforePrepareCollection();
        return parent::_prepareCollection();
    }

    /**
     * Configuring and setting collection
     *
     * @return $this
     */
    protected function _beforePrepareCollection() {
        if (!$this->getCollection()) {
            /** @var $collection \Magento\Rma\Model\ResourceModel\Rma\Grid\Collection */
            $collection = $this->_collectionFactory->create();
            $this->setCollection($collection);
        }
        return $this;
    }

    /**
     * Prepare grid columns
     *
     * @return \Magento\Rma\Block\Adminhtml\Rma\Grid
     */
    protected function _prepareColumns() {
        parent::_prepareColumns();
        $this->addColumn(
                'token_number',
                [
                    'header' => __('Token Number'),
                    'index' => 'token_number',
                    'header_css_class' => 'col-name',
                    'column_css_class' => 'col-name'
                ]
        );

        
        return $this;
    }

    /**
     * Prepare massaction
     *
     * @return $this
     */
    protected function _prepareMassaction() {
        $this->setMassactionIdField('entity_id');
        $this->getMassactionBlock()->setFormFieldName('entity_ids');

        $this->getMassactionBlock()->addItem(
                'status',
                [
                    'label' => __('Close'),
                    'url' => $this->getUrl($this->_getControllerUrl('close')),
                    'confirm' => __(
                            'You have chosen to change status(es) of the selected RMA requests to Close.'
                            . ' Are you sure you want to continue?'
                    )
                ]
        );

        return $this;
    }

    /**
     * Get Url to action
     *
     * @param  string $action action Url part
     * @return string
     */
    protected function _getControllerUrl($action = '') {
        return '*/*/' . $action;
    }

    /**
     * Retrieve row url
     *
     * @param \Magento\Framework\DataObject $row
     * @return string
     */
    public function getRowUrl($row) {
        return $this->getUrl($this->_getControllerUrl('edit'), ['id' => $row->getId()]);
    }

}