Magento 2 Undefined Index Notice in EavAttribute.php – Fix Guide

use Magento\Eav\Setup\EavSetupFactory;
use Magento\Store\Model\StoreManagerInterface;

declare:

protected $_eavSetupFactory;

constructor :

public function __construct(
    \Magento\Eav\Setup\EavSetupFactory $eavSetupFactory,
    \Magento\Store\Model\StoreManagerInterface $storeManager,
    \Magento\Catalog\Model\ResourceModel\Eav\Attribute $attributeFactory,
    \Magento\Framework\ObjectManagerInterface $objectmanager,
    ModuleDataSetupInterface $setup,
    \Magento\Catalog\Model\ProductFactory $productloader
) {
    $this->_eavSetupFactory = $eavSetupFactory;
    $this->_storeManager = $storeManager;
    $this->_attributeFactory = $attributeFactory;
    $this->_objectManager = $objectmanager;
    $this->setup = $setup;
    $this->_productloader = $productloader;
}

execute methode :

public function execute(EventObserver $observer)
{
    /** @var $brand \Ktpl\Brand\Model\Brand */
    $brand = $observer->getEvent()->getBrand();
    $option_id = "";

    $data = [];
    $attribute_arr = [$brand['brand_id'] => $brand['brand_title']];
    $optionTable = $this->setup->getTable('eav_attribute_option');
    $attributeInfo=$this->_attributeFactory->getCollection()
           ->addFieldToFilter('attribute_code',['eq'=>"shop_by_brand"])
           ->getFirstItem();

    $attribute_id = $attributeInfo->getAttributeId();

    $eavAttribute = $this->_objectManager->create('Magento\Eav\Model\Config');

    $option=array();
    $option['attribute_id'] = $attributeInfo->getAttributeId();
    $option['value'] = array(0=>array()); // 0 means "new option_id", other values like "14" means "update option_id=14" - this array index is casted to integer

    $storeManager = $this->_objectManager->get('Magento\Store\Model\StoreManagerInterface');
    $stores = $storeManager->getStores();
    $storeArray[0] = "All Store Views";       

    foreach ($stores  as $store) {
        $storeArray[$store->getId()] = $store->getName();
    }


    if (empty($brand['optionId'])) {
        foreach($attribute_arr as $key => $value){
            $option['value'][0][0]=$value;
                foreach($storeArray as $storeKey => $store){
                    $option['value'][0][$storeKey] = $value;
                }                
        }
    }
    else
    {
        foreach($attribute_arr as $key => $value){
                foreach($storeArray as $storeKey => $store){
                    $option['value'][$brand['optionId']][$storeKey] = $value;
                }                
        }
    }

    $eavSetup = $this->_eavSetupFactory->create();
    $eavSetup->addAttributeOption($option)

}

To change the display type to Text Swatch, navigate to

Dashboard > Stores > Attributes > Product

then find the 'size' attribute from the table.

Change the "Catalog Input Type for Store Owner" to Text Swatch

You should now see a new column appear in the Manage Swatch section.

Add the values that you would like to show inside the swatches, then click Save.

All items that use the size attribute will now display a text swatch instead of a drop-down menu.