WordPress custom endpoints and Breadcrumb NavXT.

functions.php

<?php

/**
 * WordPress custom endpoints breadcrumbs.
 */
class WordPressCustomEndpointsBreadcrumbs {
	/**
	 * Setup.
	 */
	public function setup() {
		// Actions
		add_action( 'bcn_before_fill', array( $this, 'bcn_before_fill' ) );
	}

	/**
	 * Breadcrumb NavXT before fill.
	 *
	 * @param bcn_breadcrumb_trail $trail
	 */
	public function bcn_before_fill( $trail ) {
		if ( ! method_exists( $trail, 'add' ) ) {
			return;
		}

		if ( ! class_exists( 'bcn_breadcrumb' ) ) {
			return;
		}

		$endpoint = _x( 'photos', 'endpoint', 'custom-text-domain' );

		$value = get_query_var( $endpoint, null );

		if ( null === $value ) {
			return;
		}

		if ( ! empty( $value ) ) {
			$trail->add( new bcn_breadcrumb(
				$value,
				null,
				array(
					'custom-photo',
				),
				null,
				null
			) );
		}

		$trail->add( new bcn_breadcrumb(
			__( 'Photos', 'custom-text-domain' ),
			null,
			array(
				'custom-photos',
			),
			trailingslashit( get_permalink() . $endpoint ),
			null
		) );

		if ( ! has_action( 'bcn_breadcrumb_url', array( $this, 'bcn_breadcrumb_url' ) ) ) {
			add_action( 'bcn_breadcrumb_url', array( $this, 'bcn_breadcrumb_url' ), 10, 3 );
		}
	}

	/**
	 * Breadcrumb NavXT breadcrumb URL.
	 *
	 * @see https://github.com/mtekk/Breadcrumb-NavXT/blob/v5.7.1/class.bcn_breadcrumb.php#L121
	 * @param string $url
	 * @param string $type
	 * @param string $id
	 * @return string
	 */
	public function bcn_breadcrumb_url( $url, $type, $id ) {
		if ( null !== $url ) {
			return $url;
		}
		
		$post_type = 'object';

		if ( in_array( 'post-' . $post_type, $type ) ) {
			return get_permalink( $id );
		}

		return $url;
	}
}

$wp_custom_endpoints_breadcrumbs = new WordPressCustomEndpointsBreadcrumbs();
$wp_custom_endpoints_breadcrumbs->setup();