Drupal Form:want to show previous form value as default_value on page

Question

My Goal is if user is submitting this form with \"Product Name\" value as \"YYY\". On submit page should reload but this time \"Product Name\" should show previous valye as

Answer 1

I usually solve this by putting the submitted value in the $_SESSION variable in the submit hook. Then the next time the form is loaded, I check the $_SESSION variable for the appropriate key, and put the value into the #default_value slot if there's anything present.