Returns a form to configure settings for the formatter.
Invoked from \Drupal\field_ui\Form\FieldInstanceEditForm to allow administrators to configure the formatter. The field_ui module takes care of handling submitted form values.
array $form: The form where the settings form is being included in.
array $form_state: An associative array containing the current state of the form.
array The form elements for the formatter settings.
Overrides FormatterBase::settingsForm
public function settingsForm(array $form, array &$form_state) {
$elements['link'] = array(
'#title' => t('Link label to the referenced entity'),
'#type' => 'checkbox',
'#default_value' => $this
->getSetting('link'),
);
return $elements;
}