using form_state->set() inside ajax callback but cannot get the value back outside the callback

Question

I want to add some arbitrary variable to store it in the form_state and use it again so in one of my ajax callback functions I set a property named var:

public function MyFunctionCallback(array &$form, FormStateInterface &$form_state) {
....
$terms = array('1'=>'one','2'=>'two');
$form_state->set('var', $terms);
....
}

it works and the storage array of the form_state has var element

unfortunately when trying to get the var back inside another callback function it returns null. actually with debugging the storage array of the form_state is empty

public function MyOtherFunctionCallback(array &$form, FormStateInterface &$form_state) {
....
$terms = $form_state->get('var');
....
}

Answer 1

You can't change $form or $form_state in an ajax callback. There is no more code coming after the callback, that could process this. The only purpose of the ajax callback is to prepare and return an ajax response.

Answer 2

As 4k4 mentioned, you cannot change the form state inside an ajax callback function.

You can, however, change it in the ajax button submit function.

$form['ajax_button']['#submit'][] = [static::class, 'ajaxButtonSubmit'];

public static function ajaxButtonSubmit($form, $form_state) {
  //...
}

Answer 3

I would like to avoid using PHP session variables here since it is easy to get mixed with other forms. Especially if the user wants to keep this form open and tried to open another form.

Instead of PHP session variables, you may try to change the logic and move your code to a validation callback for the whole form. And from there you can set form state values.

$form['#validate'][] = '::handleInputs';

Since probably what you need is part of validating the user inputs and showing specific options depend on user inputs.