ACF Integration with Fallback

There are a few issues with your code:

1. Your first get_field() call won’t work as you expect it to.

If you check the documentation of the get_field() function you’ll notice that it takes three parameters:

• The field name (required.)
• The post/page ID (optional.)
• Format value (optional.)

If the second parameter (the ID) is not provided, the get_field() function will default to the current post/page.

Since you’re not passing the $post_id parameter to get_field(), this function will attempt to retrieve the page_gallery field from the current post/page. If you’re viewing the homepage, for example, chances are the function will return null/false and in consequence none of your popular posts will display the first gallery image.

Likewise, if you’re currently viewing a post and said post does have a image gallery assigned to it then all of your popular posts will display the same image: remember, get_field() will default to the current post ID if you don’t explicitly provide an ID as a second parameter.

So, to make sure your code works as intended, your first call to get_field() should look like this instead:

$gallery = get_field('page_gallery', $post_id);

2. You’re always calling the get_field() function in your code without checking first whether the {gallery_featured_image} tag is there or not.

If you (or someone else) ever remove the {gallery_featured_image} tag from your HTML code the filter hook will still call the get_field() function, making several database read operations (one per popular post per page load) even though it might not be needed anymore which is a waste of server resources and might even have a performance impact under certain conditions.

To avoid all that make sure to check first whether you need to call the get_field() function or not by checking whether the {gallery_featured_image} is present, like so:

// Replace custom content tag {gallery_featured_image} 
// with an actual gallery_featured_image
if ( false !== strpos($html, '{gallery_featured_image}') ) {
    $gallery = get_field('page_gallery', $post_id);

    // Rest of the code goes here
}

return $html;

3. You shouldn’t be using a third party plugin’s filter hook to set the post thumbnail of a post.

The reason for this is that if someone ever decides to disable WordPress Popular Posts for some reason (or even replace it with a different plugin), then the code you’re using to automatically assign a featured image to a post from the gallery if it doesn’t have one already will stop working, then you will get angry calls/emails from the site owner (assuming it’s not you haha) and you’ll have to spend additional time trying to debug the issue only to realize that the problem happened because WPP isn’t active anymore.

This kind of stuff should be done via your theme’s functions.php file or using a site specific plugin.

Also, and for performance reasons, you’ll want to do this using a different hook. For example, I’d do this via the save_post hook to make sure that automatic featured image assignments only happen whenever someone creates and/or edits a post. The way you have it now in your code, featured images would be automatically assigned on every page load (when someone visits any page of the website where your popular post list is displayed) which -as you may already tell- might not be great for performance under certain circumstances, especially if your website is a high traffic one.

So, with all that in mind, and assuming that gallery_featured_image is a regular ACF Image field, your code becomes this (untested, you may need to tweak stuff around):

/**
 * Parses custom content tags in WordPress Popular Posts.
 *
 * @param  string $html The HTML markup from the plugin.
 * @param  integer $post_id The post/page ID.
 * @return string
 */
function wpp_parse_tags_in_popular_posts($html, $post_id)
{
    // Replace custom content tag {gallery_featured_image} 
    // with an actual gallery featured image
    if ( false !== strpos($html, '{gallery_featured_image}') ) {
        $image = null;

        // Get the gallery_featured_image from ACF
        $gallery_featured_image = get_field('gallery_featured_image', $post_id);
        
        // We have a Gallery Featured Image set
        if (
            is_array($gallery_featured_image) 
            && ! empty($gallery_featured_image)
        ) {
            $url = $gallery_featured_image['url'];
            $alt = esc_attr($gallery_featured_image['alt']);
            $image = '<img src="' . $url . '" alt="' . $alt . '">';
        } elseif ( is_numeric($gallery_featured_image) ) {
            $size = 'full';
            $image = wp_get_attachment_image($gallery_featured_image, $size);
        }
        // No featured gallery image found, fallback to first gallery image
        else {
            $gallery = get_field('page_gallery', $post_id, false);
            
            // We have a gallery set, get the first image
            if ( is_array($gallery) && ! empty($gallery) ) {
                $first_image = $gallery[0];
                $url = $first_image['url'];
                $alt = esc_attr($first_image['alt']);
                $image =  '<img src="' . $url . '" alt="' . $alt . '">';
            }
        }

        // We found an image, let's display it
        if ( $image ) {
            // Replace {gallery_featured_image} with the gallery_featured_image 
            // returned by ACF
            $html = str_replace('{gallery_featured_image}', $image, $html);
        }
        // No gallery_featured_image found, remove the content tag from output
        else {
            $html = str_replace('{gallery_featured_image}', '', $html);
        }
    }

    return $html;
}
add_filter("wpp_parse_custom_content_tags", "wpp_parse_tags_in_popular_posts", 10, 2);

Feel free to add back your set_post_thumbnail() call if you want to (but I don’t recommend it.)

• This reply was modified 5 years, 10 months ago by Hector Cabrera. Reason: Fixed typo
• This reply was modified 5 years, 10 months ago by Hector Cabrera. Reason: Fixed in code