For some reason, there are multiple functions in WordPress that do similar things but require different approaches. On the surface, you’d think the admin_body_class function would work the same as the body_class function, but you’d be wrong.
When you modify the body_class function, you hook into the filter like this:
add_filter( 'body_class', 'category_id_class' );
// add category nicenames in body and post class
function category_id_class( $classes ) {
global $post;
foreach ( ( get_the_category( $post->ID ) ) as $category ) {
$classes[] = $category->category_nicename;
}
return $classes;
}
If you break that down, you’ll notice that adding a new class name requires extending the $classes array. Straightforward enough, though for some reason when you attempt to work with the admin_body_class function, this approach causes the following error:
Fatal error: [] operator not supported for strings
That’s because it uses a string instead of an array. As long as your aware of this difference, working with the admin_body_class function is just as straightforward.add_filter( 'admin_body_class', 'custom_admin_body_class' );
function custom_admin_body_class( $classes ) {
$classes .= 'custom-class';
return $classes;
}
I’ve found the above filter useful when I needed to customize the admin after I activated a plugin. With a simple check, the function added a class name to the admin body tag which made it easier for me to use CSS on the page.
