How to get the name of a field?

Question

I'm on hook_form_alter for the config edit form. The code runs for all fields, but it's critical that the code figures out the name of the field it is on.

When I load the formobject, I can see the field_name perfectly when I print_r the array. But I can't figure out how to pull it out. Something like $name=$field['field_name']

The field name is 'field_plan_purpose' I need to get that in a variable in the code.

My code minus all of things I've tried:

$field = $form_state->getFormObject()->getEntity();
print '<pre>';
print_r($field);
print '</pre>';

Here is the top part of the array that gets printed:

Drupal\field\Entity\FieldConfig Object
(
    [deleted:protected] => 
    [fieldStorage:protected] => Drupal\field\Entity\FieldStorageConfig Object
        (
            [id:protected] => node.field_plan_purpose
            [field_name:protected] => field_plan_purpose <--- HOW DO I GET THIS
            [entity_type:protected] => node
            [type:protected] => text_long
            [module:protected] => text
            [settings:protected] => Array
                (
                )

            [cardinality:protected] => 1
            [translatable:protected] => 1
            [locked:protected] => 
            [persist_with_no_fields:protected] => 
            [custom_storage] => 
            [indexes:protected] => Array
                (
                )

            [deleted:protected] => 
            [schema:protected] => 
            [propertyDefinitions:protected] => Array
                (...

As you can see, 'field_name' is in there. Does anyone know how I can pull that out and reference it directly?

A few things I've tried:

    // print_r($field->getEntityKey('#field_name'));
    // getEntityType()->getKey('field_name')
    // $field['field_name']  $field['field_name:protected']
    // $field['id']
    // $field->getKey('field_name')
    // $field->definition['field_name'];
    // print_r($field->definition);

EDITED ******* SOLUTION

/**
 * Implements hook_form_alter().
 */
function my_module_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {

   $field = $form_state->getFormObject()->getEntity();
   $field_name = $field->getName();
   print $field_name;

}

Answer 1

FieldConfigBase has a method named getName(). That will retrieve the field name:

public function getName() {
  return $this->field_name;
}