How to get value from FlexForm to Controller

Question

I'm practicing on a very easy Extbase Extension and used a FlexForm to get three formula fields.
One of them is called "code" which should go to the EmbedderController.php and then to the viewer List.html.

I checked all tutorials I could find.

I don't understand how to get the FlexForm-value "code" into my Controller.
I get an empty page or don't get any value.

This is my FlexForm: Embedder.xml

<T3DataStructure>
        <meta type="array">
                <langChildren>0</langChildren>
                <langDisable>1</langDisable>
        </meta>
        <ROOT>
                <type>array</type>
                <el>
                        <settings.code>
                                <TCEforms>
                                        <label>Video Code</label>
                                        <config>
                                                <type>input</type>
                                                <size>20</size>
                                                <max>30</max>
                                                <eval>trim</eval>
                                        </config>
                                </TCEforms>
                        </settings.code>
                        <settings.width>
                                <TCEforms>
                                        <exclude>1</exclude>
                                        <label>Breite in Pixel</label>
                                        <config>
                                                <type>input</type>
                                                <size>10</size>
                                                <max>10</max>
                                                <eval>trim</eval>
                                        </config>
                                </TCEforms>
                        </settings.width>
                        <settings.height>
                                <TCEforms>
                                        <exclude>1</exclude>
                                        <label>Höhe in Pixel</label>
                                        <config>
                                                <type>input</type>
                                                <size>10</size>
                                                <max>10</max>
                                                <eval>trim</eval>
                                        </config>
                                </TCEforms>
                        </settings.height>
                </el>
        </ROOT>
</T3DataStructure>

And this is my EmbedderController.php

<?php
namespace HhuMediathek\Hhumediathek\Controller;
     
/**
 * EmbedderController
 */
class EmbedderController extends \TYPO3\CMS\Extbase\Mvc\Controller\ActionController {
     
        /**
         * embedderRepository
         *
         * @var \HhuMediathek\Hhumediathek\Domain\Repository\EmbedderRepository
         * @inject
         */
        protected $embedderRepository = NULL;
     
        /**
         * action list
         *
         * @return void
         */
        public function listAction() {
                $this->settings['code'];
        }
}

And this is the viewer List.html

<f:layout name="Default" />
<f:section name="main">
<iframe width='570' height='321' style='width: 570px; height: 321px; border: 1px solid #ccc;' src='//xxx.de/embed/{code}' frameborder='0' allowfullscreen></iframe>
    </f:section>

Answer 1

Okay I could figure it out myself. For people who struggle with the same problem as I did:

My mistake was, that I didn't need the line $this->settings['code']; in the Controller at all but write {settings.code} in the viewer List.html instead of just {code}. It's completly different than I read it in my book and some tutorials but this actually worked.

Answer 2

The assignment of the view parameter is missing. Therefore change

public function listAction() {
    $this->settings['code'];
}

to

public function listAction() {
    $this->view->assign('code', $this->settings['code']);
}

This way {code} should be available in the view.