I’m using baseFieldDefinitions to create my custom entity form. With gracious help here, I’ve been able to successfully generate a radio button on the form which lets the user select what view mode to use for the display.

Goal: Get the selected value from the radio button on the form and use it to reset the view mode for the display.

Problem: Other than my general confusion, I believe I have a cache issue when invoking the hook to alter the view mode. I’d like to think I was finally able to overcome the array value to single value assignment problems.

I added this code into MY-MODULE.module:

/**  * Implements hook_entity_view_mode_alter().  */ function nfl_entity_view_mode_alter(&$view_mode, DrupalCoreEntityEntityInterface $entity, $context) {     // Change the view mode to the value selected via radio button on the form.      if ($entity->getEntityTypeId() == 'nfl_fact'  ) {  /*<-- restrict to custom entity */          $change_to_view_mode = $entity->change_view->value;  /*<-- get the lowercase value -- not Initial Cap Label  */          drupal_set_message(sprintf('<pre> change_to_view_mode %s</pre>', print_r($change_to_view_mode, TRUE)));          drupal_set_message(sprintf('<pre> view_mode before %s</pre>', print_r($view_mode, TRUE)));           //  $view_mode = $change_to_view_mode;  /*<--- reassign view mode here -didn't work*/         $entity->view_mode[LANGUAGE_NONE][0]['value'] = $val[0]->change_to_view_mode;  /* <-- reassign */         $entity->save();          drupal_set_message(sprintf('<pre> view_mode after reassignment %s</pre>', print_r($view_mode, TRUE)));      } } 

I added some drupal_set_message entries to reassure myself that I was getting the variable values changed.

<pre> change_to_view_mode standard</pre> <pre> view_mode before full</pre> <pre> view_mode after reassignment standard</pre> Cache cleared. 

When I click on my link from the viewlist builder, I don’t get the display. I get White Screen of Death with the error in the PHP log:

(first few lines)

[29-Sep-2018 02:15:53 UTC] TypeError: Argument 1 passed to DrupalCoreFormOptGroup::flattenOptions() must be of the type array, null given,     called in C:wampwwwdrupal8webcoremodulesoptionssrcPluginFieldFieldFormatterOptionsDefaultFormatter.php on line 40     in C:wampwwwdrupal8webcorelibDrupalCoreFormOptGroup.php on line 23 #0 C:wampwwwdrupal8webcoremodulesoptionssrcPluginFieldFieldFormatterOptionsDefaultFormatter.php(40): DrupalCoreFormOptGroup::flattenOptions(NULL) #1 C:wampwwwdrupal8webcorelibDrupalCoreFieldFormatterBase.php(80): DrupaloptionsPluginFieldFieldFormatterOptionsDefaultFormatter->v 

I’m confused. Also am open to guidance on how to better format this question if it looks too goofy 😉