Angular Material(7.3.7) stepper without expanding the first step

Question

I want to have a angular material stepper with first step is closed(not expanded). On a form validation or a on input box validation I want to expand the first step. How can I do that? second, third steps i can do with "this.stepper.next();" or "this.step++, this.step--" etc.

Answer 1

As a temporary solution I hide the content of the first stepper until my form elements validate.