Check if a post has a specific Category

Make sure you’re accessing the global $post variable first:

global $post;
if ( in_category( 'uncategorized', $post->ID ) ) :

If you’re inside the loop (between while( have_posts() ) : the_post(); and endwhile; you can just use get_the_ID():

in_category( 'uncategorized', get_the_ID() );

First thank you, but I’m not inside a loop, I’m getting the post object from other function.

Can you share that function?

Ok, I modified Ryan Fugate example on Adding Custom Notifications to buddypress. I wanted to add posts notifications and it worked fine, except when I tried to filter them. First you need to know how I want to filter them. – I’ve a profile field named ‘Field’ which is a dropdown list with 5 options. – I have also 5 post categories with the exact names of the ‘Field’ values. – When a post is added, If it has (e.g. A,B,C) categories I want a notification for every user who has his ‘Field’ value is equal to A,B or C.
Here is the full code:

function custom_filter_notifications_get_registered_components( $component_names = array() ) {
  if ( ! is_array( $component_names ) ) {
    $component_names = array();
  }
  array_push( $component_names, 'custom' );
  return $component_names;
}
add_filter( 'bp_notifications_get_registered_components', 'custom_filter_notifications_get_registered_components' );
function custom_format_buddypress_notifications( $action, $item_id, $secondary_item_id, $total_items, $format = 'string' ) {
  if ( 'custom_action' === $action ) {
    $post = get_post( $item_id );
    $recent_author = get_user_by( 'ID', $post->post_author );
    $author_display_name = $recent_author->display_name;
    $custom_title = $author_display_name . ' has posted a new post: ' . get_the_title($post);
    $custom_text = $author_display_name. ' has posted a new post: ' . get_the_title($post);
    // WordPress Toolbar
    if ( 'string' === $format ) {
      $return = apply_filters( 'custom_filter', '<a href="' . esc_url( get_permalink( $post ) ) . '" title="' . esc_attr( $custom_title ) . '">' . esc_html( $custom_text ) . '</a>', $custom_text, $custom_link );
    // Deprecated BuddyBar
    } else {
      $return = apply_filters( 'custom_filter', array(
        'text' => $custom_text,
        'link' => $custom_link
      ), $custom_link, (int) $total_items, $custom_text, $custom_title );
    }

    return $return;

  }

}

add_filter( 'bp_notifications_get_notifications_for_user', 'custom_format_buddypress_notifications', 10, 5 );
function bp_custom_add_notification( $post_id, $post_object ) {

  $args = array(
  'blog_id'      => $GLOBALS['blog_id'],
  'role'         => 'employer',
  'role__in'     => array(),
  'role__not_in' => array(),
  'meta_key'     => '',
  'meta_value'   => '',
  'meta_compare' => '',
  'meta_query'   => array(),
  'date_query'   => array(),
  'include'      => array(),
  'exclude'      => array(),
  'orderby'      => 'login',
  'order'        => 'ASC',
  'offset'       => '',
  'search'       => '',
  'number'       => '',
  'count_total'  => false,
  'fields'       => 'all',
  'who'          => ''
 );
  $all_users = get_users($args);

foreach ($all_users as  $user) {
      $acc_type = xprofile_get_field_data('Field', $user->ID);
         if (in_category($acc_type, $post_object->ID)) {
            bp_notifications_add_notification( array(
          'user_id'           => $user->ID,
          'item_id'           => $post_id,
          'component_name'    => 'custom',
          'component_action'  => 'custom_action',
          'date_notified'     => bp_core_current_time(),
          'is_new'            => 1,
      ) );
         }

}

}
add_action( 'wp_insert_post', 'bp_custom_add_notification', 99, 2 );

PS: It works without the IF STATEMENT.

Does it work if you change

if (in_category($acc_type, $p_id)) {

to

if (in_category($acc_type, $post_id)) {

?

No, it doesn’t.

Can I make the $post object global and access it directly? Because I get the Id in custom_format_buddypress_notifications() Function.

I’m not sure what the global $post variable would be at that point, but your hook apparently passes in the the post object, so $post_object->ID should work. But if that worked $post_id should also work.

Probably not relevant, but try casting it to an integer:

if (in_category($acc_type, (int) $post_object->ID)) {
if (in_category($acc_type, (int) $post_id)) {

Are you sure $acc_type always returns a category ID, name or slug?

Thanks keesiemeijer, but I already checked this (the casting). $acc_type returns a string with a category name.

Jacob Peattie, I cant get it work either way.

Can you add this to your code and then share with us what the error log says:

error_log( 'in_category(' . $acc_type . ', ' . $post_object->ID . ')' );

[12-Aug-2016 12:26:14 UTC] in_category(Research, 731)
[12-Aug-2016 12:26:14 UTC] in_category(Services, 731)
[12-Aug-2016 12:26:14 UTC] in_category(Technology and IT, 731)
[12-Aug-2016 12:26:14 UTC] in_category(Administration, 731)
[12-Aug-2016 12:26:14 UTC] in_category(Research, 731)

Everything seems perfectly ok. The only issue I can imagine is if the category names don’t actually match those strings.

What exactly isn’t working? The notification’s not appearing?

They don’t all match, I have more categories in the extra field. But I have many matching categories like Research and Services for example. The If must return TRUE when it examines those matching ones. When I passed a post id (number) it worked.

Yeah I don’t get the notification.