// BasePresenter
public function beforeRender()
    {
        parent::beforeRender();

        if ($this->isAjax()) {
            $this->invalidateControl('flashmessage');
        }
    }

// @layout.latte
{snippet flashmessage}
                <div n:foreach="$flashes as $flash" class="flash {$flash->type}">{$flash->message}</div>
            {/snippet}

// Presenter
if ($this->isAjax()) {
                $this->flashMessage('test',  'error');
            }