如何在Vala中使用Qt GUI？

using Qt;
using System;

class MainWidget : QWidget {
  Q_OBJECT

public:
  MainWidget(QWidget *parent = nullptr) : QWidget(parent) {}

public slots:
  void on_button_clicked() {
    QLabel *label = new QLabel("Hello, World!");
    label->setAlignment(Qt::AlignCenter);
    label->setWordWrap(true);
    label->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Minimum);
    label->show();
  }
};

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);

  Qt::WindowFlags flags = Qt::WindowStaysOnTopHint;
  flags |= Qt::FramelessWindowHint;
  flags |= Qt::Dialog;
  flags |= Qt::Tool;

  MainWidget mainWidget;
  mainWidget.setWindowTitle("Vala Qt GUI Example");
  mainWidget.setGeometry(100, 100, 400, 300);
  mainWidget.setFixedSize(400, 300);
  mainWidget.show();

  return app.exec();
}

valac your_file_name.vala --pkg qt --link-flags -lQtCore -lQtCored