TYPO3 : adding a FlexForm to an Extbase Extension

ext_tables.php

<?php
defined('TYPO3_MODE') || die('Access denied.');

call_user_func(
    function()
    {
        \TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin(...
        \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addStaticFile(...
        \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addLLrefForTCAdescr(....
        \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::allowTableOnStandardPages(...

    }
);

////////////////////////////////////////////////////////////////////////////////////////////////
$extensionName = \TYPO3\CMS\Core\Utility\GeneralUtility::underscoredToUpperCamelCase($_EXTKEY);
$pluginSignature = strtolower($extensionName) . '_my_plugin_namet';
$TCA['tt_content']['types']['list']['subtypes_addlist'][$pluginSignature] = 'pi_flexform';
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPiFlexFormValue($pluginSignature, 'FILE:EXT:'.$_EXTKEY.'/Configuration/FlexForms/my_plugin_name.xml');

my_plugin_name.xml

<T3DataStructure>
	<sheets> 
		<page1>
			<ROOT>
				<TCEforms>
					<sheetTitle>Page 1</sheetTitle>
				</TCEforms>
				<type>array</type>
				<el>
          				...
				</el>				
			</ROOT>
		</page1>
		<page2>
      			...
		</page2>
	</sheets>
</T3DataStructure>

MyController.php

class MyController extends \TYPO3\CMS\Extbase\Mvc\Controller\ActionController
{
    ...
    private function _getFlexFormOptions()
    {
        $this->contentObj = $this->configurationManager->getContentObject();
        $piFlexForm = $this->contentObj->data['pi_flexform'];
        $options = \TYPO3\CMS\Core\Utility\GeneralUtility::xml2array($piFlexForm);
        return $options;
    }
}