improve qml demo

Zhao Yuhang

2024-05-08 85e783997ffd9629cdaef44b7d482f23c8ca49cb

 examples/mainwindow/mainwindow.h

@@ -30,6 +30,8 @@
protected:
    bool event(QEvent *event) override;

    void closeEvent(QCloseEvent *event) override;

private:
    void installWindowAgent();
    void loadStyleSheet(Theme theme);