protected function prepareKeys($models)
    {
        if ($this->key !== null) {
            $keys = [];
            foreach ($models as $model) {
                if (is_string($this->key)) {
                    $keys[] = $model[$this->key];
                } else {
                    $keys[] = call_user_func($this->key, $model);
                }
            }

            return $keys;
        }

        return array_keys($models);
    }
protected function prepareKeys($models)
    {
        if ($this->key !== null) {
            $keys = [];
            foreach ($models as $model) {
                if (is_string($this->key)) {
                    $keys[] = $model[$this->key];
                } else {
                    $keys[] = call_user_func($this->key, $model);
                }
            }

            return $keys;
        }

        return array_keys($models);
    }
protected function prepareKeys ( $ models ) { if ( $ this -> key !== null ) { $ keys = [ ] ; foreach ( $ models as $ model ) { if ( is_string ( $ this -> key ) ) { $ keys [ ] = $ model [ $ this -> key ] ; } else { $ keys [ ] = call_user_func ( $ this -> key , $ model ) ; } } return $ keys ; } return array_keys ( $ models ) ; }
{@inheritdoc}
{