Cannot get form_state storage or protected form values to work

Question

I am building a form using formBuilder. I have tried two methods to store values across form submit/validate for usage in ajax callbacks, but have been unsuccessful in either.

The first method, was to store a value in $form_state->set('name','value'); and retreiving it in the form submit/validate handler. That returned an empty result.

The second method was to store a variable on the class itself protected $image_deltas = 0; and then when the ajax form submit/validation is triggered, $this->image_deltas++; However, when I do this, it still does not work.

The following is the code I am using.

$form['images'] = [
  '#type' => 'container',
  '#id' => 'images',
];

dpm($this->image_deltas);

for ($i=0;$i<=$this->image_deltas;$i++) {
  $form['images'][$i]['image'] = [
    '#type' => 'textfield',
    '#title' => t('Image Path:'),
  ];
}

$form['add_another'] = [
  '#type' => 'button',
  '#value' => t('Add Another Image'),
  '#ajax' => [
    'callback' => [$this, 'addAnotherImage'],
    'wrapper' => 'images',
  ],
  '#submit' => [$this, 'addAnotherImageSubmit'],
  '#limit_validation_errors' => [],
];

The form submission handler is the following.

public function addAnotherImageSubmit(&$form, FormStateInterface $form_state) {
  $this->image_deltas++;
  $form_state->setRebuild();
}

The AJAX callback is the following one.

public function addAnotherImage(&$form, FormStateInterface $form_state) {
  return $form['images'];
}

When I submit the form, dpm() prints 0 every time. The same thing happens if I use $form_state->set('image_deltas') and $form_state->get('image_deltas').

Answer 1

This:

'#submit' => [$this, 'addAnotherImageSubmit'],

Should be this:

'#submit' => [[$this, 'addAnotherImageSubmit']],

Submit handlers are only called for #type submit and not #type button, so you'll need to change the type.

You will also need to use $form_state->set(), rather than a property on the class. This is because the form class is re-instantiated for each iteration (build, validate, submit), and therefore values stored in the properties of the form class will not persist. $form_state->set() persists values, as these are stored in the database, and are repopulated for each instance of the form class (as long as you call $form_state->setRebuild() as you have done).