more information Input drop down

 

We all know that to define a drop down we do like this:   
echo elgg_view_field ([      '#type' => 'dropdown'
                                           , .......................,
                                           'options_values' => [          'dvpdurable' => elgg_echo ('............')]
                                    ]);

and now if I want to retrieve a set of objects in a drop down I do like this


$objects = elgg_list_entities ([]);

foreach($objects as $object){

$options[$object->getDisplayName()] =  $object->title;

}
$vars['class'] = elgg_extract_class($vars, ['elgg-input-object']);
$vars['options'] = $options;

echo elgg_view('input/dropdown',$vars);

my question is the following, where should we put the keys of values ​​as in the first because we:

 'key' => elgg_echo ('value')

regards