可能这不是最好的方法，因为它需要引入一个全局变量，但想法如下：

在里面Posts_in_Page 插件有2个过滤器，其中一个在输出这些项目之前启动posts_in_page_pre_loop, 输出端后一个posts_in_page_post_loop. 因此，计划是创建全局变量，该变量将设置为true 当你在这个插件的循环中false 当它在外面时，所以在摘录过滤器中，您可以检查它。

下面是如何做到这一点：

/*
 * Sets our global flag that we are inside this plugin\'s specific loop. And returns content untouched.
 */
function my_custom_set_in_posts_pages_loop($output){

    global $custom_loop_is_in_posts_in_page_post_loop;
    $custom_loop_is_in_posts_in_page_post_loop = true;

    return $output; // output is untouched we return it as is, because we only switch our flag.
}
add_filter(\'posts_in_page_pre_loop\', \'my_custom_set_in_posts_pages_loop\');

/*
 * Sets our global flag that we are inside this plugin\'s specific loop. And returns content untouched.
 */
function my_custom_set_out_of_posts_pages_loop($output){
    global $custom_loop_is_in_posts_in_page_post_loop;
    $custom_loop_is_in_posts_in_page_post_loop = false;

    return $output; // output is untouched we return it as is, because we only switch our flag.
}
add_filter(\'posts_in_page_post_loop\', \'my_custom_set_out_of_posts_pages_loop\');


function the_readmore_excerpt( $excerpt ) {
    global $custom_loop_is_in_posts_in_page_post_loop;

    if( isset($custom_loop_is_in_posts_in_page_post_loop) && $custom_loop_is_in_posts_in_page_post_loop ){
        return $excerpt. \'.. <a class="read-more" href="\'. get_permalink( get_the_ID() ) . \'">\' . __(\'Mehr lesen\', \'baskerville\') . \' &rarr;</a>\';
    }

    return $excerpt; // return default excerpt if we are not in this custom plugin\'s loop.
}

add_filter(\'get_the_excerpt\', \'the_readmore_excerpt\');

插件的过滤器挂钩来自这里https://github.com/ivycat/posts-in-page/blob/master/includes/class-page-posts.php （第364373行）