"qt is not defined" error when to create second QWebEngineView window

bool PreviewPage::acceptNavigationRequest(const QUrl &url,
                                          QWebEnginePage::NavigationType /type/,
                                          bool /isMainFrame/)
{
    // Only allow qrc:/index.html.
    if (url.scheme() == QString("qrc"))
        return true;
    QWebEngineView   *v=new QWebEngineView();
    PreviewPage *page = new PreviewPage(v);
    v->setPage(page);
    v->setUrl(QUrl("qrc:/index.html"));
    v->show();
    //QDesktopServices::openUrl(url);
    return false;
}