protected function loadAdjacentPost($direction = null)
    {
        $loadPrev = $loadNext = false;
        switch ($direction) {
            case 'prev':
                $loadPrev = true;
                break;
            case 'next':
                $loadNext = true;
                break;
            default:
                $loadPrev = $loadNext = true;
                break;
        }
        if ($loadPrev && !$this->prevPost) {
            $this->prevPost = $this->getAdjacentPost('prev', $this->get('post_type'));
        }
        if ($loadNext && !$this->nextPost) {
            $this->nextPost = $this->getAdjacentPost('next', $this->get('post_type'));
        }
    }