Multistep form loses input when visiting previous step

Question

I am developing a custom module with the ability to store data on an external database using Drupal 7 Form API. I started with the multistep form example, added few more steps and other fields.

To implement the ability to edit those data I created a class that retrieves returns an array suitable to fill the $form_state['values'] element in order to have a default value for each form element. Here follows the code I have in the form callback when going to edit my data:

if( !empty($form_state['build_info']['args'][0]) ) ) {
    $a = new ind();
    $a->get_ind( $form_state['build_info']['args'][0] );

    $form_state['values'] = get_object_vars($a);
    unset($a);
}

Problem is when I hit the previous/next buttons because of the form is being rebuilt always with the data from the class so every change in a field is lost when hitting "Previous"; suddenly every change gets lost when I click "Next" after "Previous" (fields are empty!).

How do you achieve editing with multistep form with existing data? I am stuck here attempting to put the code above at submit and previous handlers with no success.

Answer 1

I think you should add if statement with #triggering_element or #clicked_button. Example:

function PREVIOUS_STEP_submission_OR_SOME_KIND_OF_CALLBACK($form, &$form_state) {
  if($form_state['clicked_button']['#value'] == 'BACK') {
    //show_previous_step()
  }
  else {
    $a = new ind();
    $a->get_ind( $form_state['build_info']['args'][0] );

    $form_state['values'] = get_object_vars($a);
    unset($a);
    // or your logic
  }
}