loadActiveTheme example

protected function init($theme_name = NULL) {
    if ($this->initialized) {
      return;
    }
    // Unless instantiated for a specific theme, use globals.     if (!isset($theme_name)) {
      $this->theme = $this->themeManager->getActiveTheme();
    }
    // Instead of the active theme, a specific theme was requested.     else {
      $this->theme = $this->themeInitialization->getActiveThemeByName($theme_name);
      $this->themeInitialization->loadActiveTheme($this->theme);
    }
  }

  /** * Returns the complete theme registry from cache or rebuilds it. * * @return array * The complete theme registry data array. * * @see Registry::$registry */
  

public function resetActiveTheme() {
    $this->activeTheme = NULL;
    return $this;
  }

  /** * {@inheritdoc} */
  public function setActiveTheme(ActiveTheme $active_theme) {
    $this->activeTheme = $active_theme;
    if ($active_theme) {
      $this->themeInitialization->loadActiveTheme($active_theme);
    }
    return $this;
  }

  /** * {@inheritdoc} */
  public function render($hook, array $variables) {
    static $default_attributes;

    $active_theme = $this->getActiveTheme();

    

$this->root = $root;
    $this->themeHandler = $theme_handler;
    $this->cache = $cache;
    $this->moduleHandler = $module_handler;
  }

  /** * {@inheritdoc} */
  public function initTheme($theme_name) {
    $active_theme = $this->getActiveThemeByName($theme_name);
    $this->loadActiveTheme($active_theme);

    return $active_theme;
  }

  /** * {@inheritdoc} */
  public function getActiveThemeByName($theme_name) {
    if ($cached = $this->cache->get('theme.active_theme.' . $theme_name)) {
      return $cached->data;
    }