所以，从点击到调用这个PHPajax 我设法在我的modal.但是当代码到达get_post_gallery 它总是回来null.

$the_query  = new WP_Query(array(\'p\' => $pid));

if ($the_query->have_posts()) {
    while ( $the_query->have_posts() ) {
        $the_query->the_post();
        $data = \'
        <div class="post-container">
            <div id="project-content">
                <h1 class="entry-title">\' . get_the_title() . \'</h1>
                <div class="entry-content">\' . get_the_content() . \'</div>

            </div>
        </div>  
        \';

        if ( get_post_gallery( ) ) :
                $gallery = get_post_gallery(get_the_ID(), false );              
        endif;
    }
}

另一方面，该方法适用于single.php 页所以我认为这是一个上下文问题。谢谢你的帮助。

if (get_post_gallery($pid)) :
   $gallery = get_post_gallery($pid, false);
endif;