I'm creating a 3-step (3-page) form in Drupal 8. One property I use for all three pages is $continue - which triggers an exit process (redirect) if an error condition is encountered, or allows the process to continue through all three pages. Also, there is a node created during submitForm() in step 1, and the node id is needed in steps 2 and 3.
I'm struggling with exactly how to pass data of that nature through the multiple steps. Initially, the form is built, and properties can be initialized in the constructor. But after the user submits the form, that's an entirely new request, right? So doesn't the form class have to be instantiated again before the submitForm() method is invoked? If so, it doesn't seem like properties could persist from buildForm() to submitForm() and back to the buildForm() for step 2?
In Drupal 7, I had to save all values I wanted to persist into $form_state. Do I still need to do the same in Drupal 8?