Programmatically get field definition for custom user profile fields

Question

I created several custom user profile fields, including Full Name (a plain text field) and County (a List (text) field). They are displayed on the /user/#/edit form. I want to display these fields (and several others) in a different form I am generating via custom module code.

Question: Is it possible to extract the definition of a field, including its label, default value, and, in the case of County, the list of allowed values?

I imagine a field is an entity of some kind that can be extracted, but after much reading, I haven't seen how. I'm likely just not using the right terminology.

I could easily hard-code replicas of these fields in the PHP+HTML form, but I want to maintain the label, default value, list of allowable values, etc. for them in just one place--as part of the user profile. Thus, I want to extract their definitions and output them into the form I build.

Answer 1

Yes you can get field definition programmatically with field name and entity name, by using EntityFieldManager::getFieldDefinitions. For your select list how to get allowed values check this example

 $options_array = [];
    $field_name = 'field_country_list';
    $definitions = \Drupal::service('entity_field.manager')->getFieldDefinitions('custom_entity_name', 'bundle');

    if (isset($definitions[$field_name])) {
      $options_array = $definitions[$field_name]->getSetting('allowed_values');
    }

source : https://api.drupal.org/comment/63953#comment-63953

Answer 2

You can use a field widget from an entity form in a custom form as follows:

$entity_type = 'user';
$bundle = 'user';
// Alter accordingly if you are using custom form modes.
$form_mode = 'default';
$field_name = 'field_fullname';
$element_name => 'fullname';

if (!isset($form[$element_name]['#parents'])) {
  // Required widget to be embedded.
  $form[$element_name]['#parents'] = [];
}

$form_display = \Drupal::entityTypeManager()->getStorage('entity_form_display')->load($entity_type .'.' . $bundle . '.' . $form_mode);
if ($widget = $form_display->getRenderer($field_name)) {
  $items = $podcast->get($field_name)->filterEmptyItems();
  $form[$element_name] = $widget->form($items, $form, $form_state);
  $form[$element_name]['#access'] = $items->access('edit');
}

The resulting value is buried in the $form_state->getValues() array, and differs depending on the widget type, so you'll need to examine that array on submission to find the value you are looking for.