一个关于返回值的问题 [ 2.0 版本 ]

/** 
 * @param string $view the view name.
 * @param array $params the parameters (name-value pairs) that should be made available in the view.
 * These parameters will not be available in the layout.
 * @return string the rendering result.
 * @throws InvalidArgumentException if the view file or the layout file does not exist.
 */
public function render($view, $params = [])
{
    $content = $this->getView()->render($view, $params, $this);
    return $this->renderContent($content);
}

return string 类型。