Using Drupal's hook_theme() for custom theming

This is a short post on how to use Drupal's hook_theme() to customize a layout within your own custom module.

Start off with implementing the hook_theme() function in your module:

/**
 * Implements hook_theme()
 * @param type $existing
 * @param type $type
 * @param type $theme
 * @param type $path
 * @return array
 */
function mypm_theme($existing, $type, $theme, $path) {
  $themes = array(
    'chat' => array(
      'variables' => array(
        'message' => NULL,
        'author' => NULL,
        'date_posted' => NULL,
        'is_sender' => NULL,
        'product_url' => NULL,
      )
    ),
  );

  return $themes;
}

What I've declared in the function is that I have a custom theme function called "chat". It takes in 5 variables defined in the variables array. As always, remember to clear Drupal's cache once you've defined a new theme function. Now that we have declared our theme function, we'll have to implement it:

function theme_chat($variables) {
  $main_style = 'chat-holder';

  if (isset($variables['is_sender'])) {
    if ($variables['is_sender'] == TRUE) {
      $main_style .= ' chat-holder-sent';
    }
    else {
      $main_style .= ' chat-holder-received';
    }
  }
  else {
    $main_style .= ' chat-holder-received';
  }

  $output = '
';

  $output .= '
';
  $output .= $variables['author'];
  $output .= '
';

  $output .= '
';
  $output .= format_date($variables['date_posted']);
  $output .= '
';

  $output .= '
';
  $output .= nl2br(check_plain($variables['message']));
  $output .= '
';

  $output .= $variables['product_url'];

  $output .= '
';

  return $output;
}

The theme_chat function builds the HTML output based on the variables passed in. You can now use this theme function in your form or normal page callback like below:

    $chat_output .= theme('chat',
            array(
                'message' => $chat->message,
                'author' => $chat->author_name,
                'date_posted' => $chat->created,
                'is_sender' => $chat->sender,
                'product_url' => $chat->product_url,
            ));