"Drupal8表单构建元素（下拉列表）"

$form['example\_select'] = [  
  '#type' => 'select',  
  '#title' => $this->[t](https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21StringTranslation%21StringTranslationTrait.php/function/StringTranslationTrait%3A%3At/8.2.x "Translates a string to the current language or to a given language.")('Select element'),  
  '#options' => [  
    '1' => $this->[t](https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21StringTranslation%21StringTranslationTrait.php/function/StringTranslationTrait%3A%3At/8.2.x "Translates a string to the current language or to a given language.")('One'),  
    '2' => [  
      '2.1' => $this->[t](https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21StringTranslation%21StringTranslationTrait.php/function/StringTranslationTrait%3A%3At/8.2.x "Translates a string to the current language or to a given language.")('Two point one'),  
      '2.2' => $this->[t](https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21StringTranslation%21StringTranslationTrait.php/function/StringTranslationTrait%3A%3At/8.2.x "Translates a string to the current language or to a given language.")('Two point two'),  
    ],  
    '3' => $this->[t](https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21StringTranslation%21StringTranslationTrait.php/function/StringTranslationTrait%3A%3At/8.2.x "Translates a string to the current language or to a given language.")('Three'),  
  ],  
];