How to pass custom values from buildForm() to submitForm()

Question

My buildForm() method queries the database and returns data which is used to calculate default values for the form. How can I use these values in submitForm() without querying the database again?

Answer 1

Typically, the $form_state object can be used to stash that data. $form_state->getStorage() references a simple array that you can put whatever you like inside, which you can then retrieve in submitForm() the same way.

You can store values in buildForm function as follows

$form_state->set('variable_name', $value);

Inside submitForm function, you can retrieve this as

$value = $form_state->get('variable_name');

variable_name can be any name