The default controller for extension \"X\" and plugin \"X\" can not be determined

Question

Good Afternoon all.

I'm trying to make an extension for TYPO3 8.7 but I'm getting this error and I have tried everything without any luck.

ext_localconf.php

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

\TYPO3\CMS\Extbase\Utility\ExtensionUtility::configurePlugin(
    'AOE.' . $_EXTKEY,
    'AoeShowroom',
    [
        \AOE\AoeShowroom\Controller\ShoeController::class => 'list, show',
    ],
    // non-cacheable actions
    [
        \AOE\AoeShowroom\Controller\ShoeController::class => '',
    ]
);

tt_content.php

<?php

\TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin(
    'AOE.AoeShowroom',
    'AoeShowroom',
    'AOE Showroom',
    'EXT:aoe_showroom/Resources/Public/Icons/Extension.svg'
);

ShoeController.php

<?php
namespace AOE\AoeShowroom\Controller;
...
?>

If you need any other file please request.

Thanks

Answer 1

This happens because you have formerly created an extension plugin on this page. Later you have changed the former plugin into this plugin. The error message comes from the flexform field of the former plugin. Now it cannot find the controller, because the flexform does not fit to the current plugin.

Solution: Delete the flexform of this tt_content recore by a database tool, e.g. phpmyadmin. Use the id of the plugin record as uid of tt_content.

UPDATE `tt_content` SET `pi_flexform` = '' WHERE `tt_content`.`uid` = 29;

see German page