BUJ

My chosen featured image doesn’t show, why isn’t it working?

This plugin can’t guarantee that it works. That depends on the themes. Still I want to know if it fails, so contact me

Which functions can I use to display the featured image?

The plugin uses the default WordPress functions the_post_thumbnail or get_the_post_thumbnail. has_post_thumbnail will always return true. get_post_thumbnail_id will return the ID set on the post or the DFI you set.

Can I exclude a page or give it a different image?

Yes you can by using the builtin dfi_thumbnail_id filter. It will give you the post id which you can use to check against.

Don’t use a featured image on page 23

function dfi_skip_page ( $dfi_id, $post_id ) {
  if ( $post_id == 23 ) {
    return 0; // invalid id
  }
  return $dfi_id; // the original featured image id
}
add_filter( 'dfi_thumbnail_id', 'dfi_skip_page', 10 , 2 );

Use a different image for some categories

The example below only works if the post has ‘animals’ as a category. Assigning just ‘cats’ won’t work
To do that just don’t nest the if

function dfi_category ( $dfi_id, $post_id ) {
  // all which have 'animals' as a category
  if ( has_category( 'animals', $post_id ) ) {

    //sub category
    if ( has_category( 'cats', $post_id ) ) {
      return 7; // cats img
    } else if has_category( 'dogs', $post_id ) {
      return 8; // dogs img
    }

    return 6; // default animals picture
  }
  return $dfi_id; // the original featured image id
}
add_filter( 'dfi_thumbnail_id', 'dfi_category', 10, 2 );

Different image for the post_type ‘wiki’

function dfi_posttype_book ( $dfi_id, $post_id ) {
  $post = get_post($post_id);
  if ( 'wiki' === $post->post_type ) {
    return 31; // the image id
  }
  return $dfi_id; // the original featured image id
}
add_filter( 'dfi_thumbnail_id', 'dfi_posttype_book', 10, 2 );

Can I change the HTML of the image returned?

yes you can with the filter dfi_thumbnail_html.

function dfi_add_class($html, $post_id, $default_thumbnail_id, $size, $attr) {
    // add a class to the existing class list
    $attr['class'] .= ' my-class';

    return wp_get_attachment_image( $default_thumbnail_id, $size, false, $attr );
}
add_filter( 'dfi_thumbnail_html', 'dfi_add_class', 10, 5 );