listing attachments of a category?

Of course, I followed a path, but I did not reach the result, first I get all post IDs of a category with this code :

<?php 
$cat_posts = get_posts(array(
    'category' => 42,
    'numberposts' => -1
));
$parent_ids = array_map('get_post_ids', $cat_posts);
function get_post_ids($post_obj) {
    return isset($post_obj->ID) ? $post_obj->ID : false;
}

?>

and then I add $parent_ids to shortcode, but its not work!

<?php echo do_shortcode('[ajax_load_more posts_per_page="12" post_type="attachment" custom_args="post_parent:'.$parent_ids.'" post_status="inherit"]'); ?>

thanks but it doesn’t help.

below shortcode show attachments of a specific post, is there a way to add multiple ids to this code?

for example “post_parent:50,51,52” instead of “post_parent:50”, if Found a solution for this probably my problem will solved.

[ajax_load_more post_type="attachment" custom_args="post_parent:50" post_status="inherit" preloaded="true"]

this is a working WP Query, this code first get all post IDs of a category, then show attachments of that posts.

<?php 
// get all posts of a certain category
$query = new WP_Query( 
    array( 
        'cat' => 42,
        'posts_per_page' => -1,
        'fields' => 'ids'
    ));
// get all attachments of posts form previous query and show them
$image_query = new WP_Query( 
    array( 
        'post_type' => 'attachment',
        'post_status' => 'inherit',
        'post_parent__in' => $query->posts,
        'posts_per_page' => 10,
    ));
if( $image_query->have_posts() ){
while( $image_query->have_posts() ) {
$image_query->the_post();?>
	<?php $imgurl =  wp_get_attachment_image($image->ID, 'thumbnail');
	 echo '<a style="display:inline-block;" href="';
	 echo get_permalink();
	 echo '">';
	 echo $imgurl;
	 echo '</a>';?>
<?php } } ?>

I used ‘post_parent_in’ and its not working. And of course I tried a few other solutions, none of them worked!

I think it may not be possible to do this with alm