Ultimate Member: new UI and callback functions

functions.php

function um_custom_country_choices_callback() {
	// choices array.
	$countries = array(
		"FR" => "France",
		"ES" => "Spain",
		"IT" => "Italy",
	);

	return array_unique( $countries );
}

if ( UM()->is_new_ui() ) {
	function um_custom_city_choices_callback( $parent_options = array(), $parent_key = null ) {
		// choices array.
		$all_options = array(
			"FR" => array(
				"Paris"     => "Paris",
				"Marseille" => "Marseille",
				"Lyon"      => "Lyon"
			),
			"ES" => array(
				"Madrid"    => "Madrid",
				"Barcelona" => "Barcelona"
			),
		);

		// get related options for the parent field choice.
		$arr_options = array();
		if ( empty( $parent_options ) ) {
			// Show all child options for empty parent. It's for member directory filter.
			foreach ( $all_options as $k => $opts ) {
				$arr_options = array_merge( $opts, $arr_options );
			}
		} else {
			foreach ( $parent_options as $parent_option ) {
				if ( isset( $all_options[ $parent_option ] ) ) {
					$arr_options = array_merge( $arr_options, $all_options[$parent_option] );
				}
			}
		}

		return array_unique( $arr_options );
	}
} else {
	function um_custom_city_choices_callback() {
		// choices array.
		$all_options = array(
			"FR" => array(
				"Paris"     => "Paris",
				"Marseille" => "Marseille",
				"Lyon"      => "Lyon"
			),
			"ES" => array(
				"Madrid"    => "Madrid",
				"Barcelona" => "Barcelona"
			),
		);

		// Get values from the parent field, sent via the AJAX post (dynamic change parent dropdown on a page).
		$parent_options = isset( $_POST['parent_option'] ) ? $_POST['parent_option'] : array();
		if ( ! is_array( $parent_options ) ) {
			$parent_options = array( $parent_options );
		}

		// get related options for the parent field choice.
		$arr_options = array();
		if ( empty( $parent_options ) ) {
			foreach ( $all_options as $k => $opts ) {
				$arr_options = array_merge( $opts, $arr_options );
			}
		} else {
			foreach ( $parent_options as $parent_option ) {
				if ( isset( $all_options[$parent_option] ) ) {
					$arr_options = array_merge( $arr_options, $all_options[$parent_option] );
				}
			}
		}

		// Optional. Display this if there are no related options for this choice.
		if ( empty( $arr_options ) ) {
			$arr_options[] = 'No cities found';
		}

		return array_unique( $arr_options );
	}
}