do_action( 'switch_theme', string $new_name, WP_Theme $new_theme, WP_Theme $old_theme )

869	 * @since 4.5.0 Introduced the `$old_theme` parameter.870	 *871	 * @param string   $new_name  Name of the new theme.872	 * @param WP_Theme $new_theme WP_Theme instance of the new theme.873	 * @param WP_Theme $old_theme WP_Theme instance of the old theme.874	 */875	do_action( 'switch_theme', $new_name, $new_theme, $old_theme );876}877 878/**879 * Checks that the active theme has the required files.880 *881 * Standalone themes need to have a `templates/index.html` or `index.php` template file.