exampleform2.php

<?php

namespace Drupal\example\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\HtmlCommand;

/**
* Class ExampleForm.
*
* @package Drupal\example\Form
*/
class ExampleForm extends FormBase {
  
  
  /**
  * {@inheritdoc}
  */
  public function getFormId() {
    return 'example_form';
  }
  
  /**
  * {@inheritdoc}
  */
  public function buildForm(array $form, FormStateInterface $form_state) {
    
    $form['group1'] = [
      '#type' => 'container',
    ];
    
    
    $form['group2'] = [
      '#type' => 'container',
      '#access' => TRUE,
      '#prefix' => '<div id="test">',
      '#suffix' => '</div>',
    ];
    
    
    
    $form['group2']['test'] = [
      '#type' => 'submit',
      '#value' => t('Enable'),
      '#ajax' => [
        'callback' => '::testCallback',
        'wrapper' => 'test',
      ],
    ];
    
    $form['group2']['example'] = [
      '#type' => 'textfield',
      '#access' => TRUE,
      '#required' => TRUE,
    ];
    

    
    
    
    return $form;
  }
  
  /**
  * {@inheritdoc}
  */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    parent::validateForm($form, $form_state);
  }
  
  /**
  * {@inheritdoc}
  */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    // Display result.
    foreach ($form_state->getValues() as $key => $value) {
      drupal_set_message($key . ': ' . $value);
    }
    
  }
  
  public function testCallback(array &$form, FormStateInterface $form_state) {
    
    $form['group2']['example']['#access'] = TRUE;
    unset($form['group2']['test']);
    
    
    $form['group2']['form'] = [
      '#type' => 'container',
      '#attributes' => [
        'id' => 'foo',
      ]
    ];
    
    $form['group2']['form']['yolo'] = [
      '#type' => 'textfield',
      '#required' => TRUE,
      '#description' => 'haha',
    ];
    
    // Does not work if defined here
    $form['group2']['submitter'] = [
      '#type' => 'button',
      '#value' => t('Enable me'),
      '#attributes' => [
        'style' => 'display: none',
      ],
      '#ajax' => [
        'wrapper' => 'test',
        'effect' => 'fade',
        'callback' => '::doSomething',
      ],
      
    ];
    
    
    return $form['group2'];
    
  }
  
  public function doSomething(array &$form, FormStateInterface $form_state) {
    
    unset($form['group2']['submitter']);
    unset($form['group2']['test']);
    
    
    $form['group2']['blaba'] = [
      '#type' => 'html_tag',
      '#tag' => 'p',
      '#value' => 'yo',
    ];
    
    return $form['group2'];
    
    
  }
  
}