Post Object: getting featured image alt tag

• cuco

• November 12, 2020 at 11:48 pm

I need to grab the alt tag for a featured image – I know how to get it normally but when I’m displaying the post via a Post Object I just get the error:

Warning: Use of undefined constant ‘_wp_attachment_image_alt’ – assumed ‘‘_wp_attachment_image_alt’’ (this will throw an Error in a future version of PHP) in [url to template] on line 106

Below is my code (commented out bits not working):

$post_object = get_field('hp_project1');

    if( $post_object ): 

    $post = $post_object;
    setup_postdata( $post ); 

    $thumb = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'large' );
    //$thumb_id = get_post_thumbnail_id( $post->ID );
    //$thumb_alt = get_post_meta($thumb_id, ‘_wp_attachment_image_alt’, true);

This will give me the image url fine:
<?php echo $thumb[0]; ?>

but
<?php echo $thumb_alt; ?>

will not give me the alt tag, which would normally work when not grabbing it via a acf post object.

I google this for about an hour but couldn’t find anything specifically for grabbing it via Post Objects.

• cuco

• November 27, 2020 at 1:34 am

Right, I’ve finally got to the bottom of this after much googling.

The issue is $post->ID. It looks like the global $post is not accessible at that point when you’re using the standard (working code) when the variable is through a Post Object.

Changing it to this, seems to have done the trick:

$thumb = wp_get_attachment_image_src( get_post_thumbnail_id( get_the_ID() ), 'large' );
$thumb_id = get_post_thumbnail_id( get_the_ID() );