Pass argument to buidlform?

Question

So i have a simple form that extends the FormBase and when i call the form i pass it an argument, depending on what the user selects within the form itself i rebuild the form and i need to pass a new argument to the buildForm, how do i do this?

class MyForm extends FormBase {
    public function buildForm(array $form, FormStateInterface $form_state, $frv = null) {
      ...
    }
    public function validateForm(array $form, FormStateInterface $form_state) {
        ...
        if (true) {
            $form_state->setRebuild();
            $frv = 'some new string';
            // somehow pass this new $frv to the buildForm ???
        }
    }
}

Answer 1

$form_state->set() will help do this,

public function buildForm(array $form, FormStateInterface $form_state) {
  ...

  if($form_state->get('variable')){
    //do your logic
  }
}

public function validateForm(array $form, FormStateInterface $form_state) {
    ...
    $form_state->set('variable', 2);//any value


    if($form_state->get('variable')){
      $form_state->setRebuild(TRUE);
    }
}