AdminNotice.php

<?php

namespace To4Framework;

if (!defined('ABSPATH')) {
  exit;
}

/**
 * Wrapper class to display admin and debug.log messages.
 * To use, as an example for a success notifiction AdminNotice::displaySuccess($message)
 * @see https://wordpress.stackexchange.com/questions/152033/how-to-add-an-admin-notice-upon-post-save-update
 */
class AdminNotice {
  /**
   * Static property to hold our singleton instance
   *
   */
  const NOTICE_FIELD = 'to4_admin_response';

  /**
   * Retrieve stored message from options and show in admin notices, also sends message to debug.log
   * and clears 'to4_admin_response'options table field
   * @uses admin_notices hook
   * @return void
   */
  public function displayAdminNotice()
  {
      $responses = get_option(self::NOTICE_FIELD, []);

      if (!empty($responses)) {
        foreach ( $responses as $response ) {
          $message = esc_html( $response['message'] ); //isset($response['message']) ? $response['message'] : false;
          $noticeLevel = ! empty($response['notice-level']) ? esc_attr( $response['notice-level'] ) : 'notice-error';

          echo "<div class='notice {$noticeLevel} is-dismissible'><p>{$message}</p></div>";

        }
      }

      // Now we reset our options to prevent notices being displayed forever.
      if( !empty( $responses ) ) {
          delete_option(self::NOTICE_FIELD, []);
      }
  }

  /**
   * Updates 'to4_admin_response' options field with message, and sets notice type to 'error'
   * @param  string $message
   * @return void
   */
  public static function displayError($message)
  {
      self::updateOption($message, 'notice-error');
  }

  public static function displayWarning($message)
  {
      self::updateOption($message, 'notice-warning');
  }

  public static function displayInfo($message)
  {
      self::updateOption($message, 'notice-info');
  }

  public static function displaySuccess($message)
  {
      self::updateOption($message, 'notice-success');
  }

  /**
   * Store response message in options temporarily for display in admin_notices hook
   * @param  string $message
   * @param  string $noticeLevel
   * @return void
   */
  protected static function updateOption($message, $noticeLevel) {

      $response = get_option( self::NOTICE_FIELD, [] );

      // We add our new notice.
      array_push( $response, [
              'message' => sanitize_text_field($message),
              'notice-level' => sanitize_text_field($noticeLevel),
          ] );

      // Then we update the option with our notices array
      update_option(self::NOTICE_FIELD, $response );
  }

  /**
   * Prints a message to the debug file that can easily be called by any method.
   * @param mixed $message an object, array, string, number, or other data to write to the debug log
   *
   */
  public static function log($message)
  {
    error_log(print_r($message, true));
  }

}