<?= $form->field($model, 'categories[]')->dropDownList(Category::getCategoryList(), [
'multiple' => true,
'options' => $movie->getCategorySelected(),
]
) ?>
array(2) { [5]=> array(1) { ["selected"]=> bool(true) } [27]=> array(1) { ["selected"]=> bool(true) } }
'options'=> [ 'options'=>$movie->getCategorySelected()
]