[Solved] QMainWindow subclass not receiving winEvents unless QMessageBox is called

Hello all,

I'm new to Qt (4.8.1 for Desktop + MSVC2010) and also just starting to get a handle on C++, and I'm trying to interact with a 3rd party driver DLL that sends Events to a HWDN (which I attempt to set via MainWindow::effectiveWinId() ). This has been working, though apparently only by chance, as inside my MainWindow, before setting said HWND, I called created a QMessageBox.
My MainWindow is a regular UI-Designer subclassed QMainWindow:

Code:

---

namespace Ui {
    class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    virtual bool winEvent( MSG* message, long* result );
    ~MainWindow();
 
private:
    Ui::MainWindow *ui;
....
    void installmessages();
 
private slots:
     void on_freezeButton_clicked();
 
};

---

The code in MainWindow::installmessages();

Code:

---

qDebug() << "before";
    qDebug() << MainWindow::effectiveWinId() ;
 
// *
    qDebug() << "messagebox";
    QMessageBox::information(   this,
                                tr("Messagebox title"),
                                tr("WinID %1").arg( (long) MainWindow::effectiveWinId() )
                             );
 
// */
    qDebug() << "after";
    qDebug() << MainWindow::effectiveWinId() ;
 
....
 
[call to proprietary library with MainWindow::effectiveWinId() as parameter]

---

results in this output

Code:

---

before 
0x0 
messagebox  [the output is "WinID 0"]
after 
0x17046a

---

So with message box, my program works since I get a valid ID and thus receive messages.
Why is the WinID valid only when the MessageBox is run?

in which method are your qDebug() outputs?
And show the rest, the code (where the debug outputs are) only shows that you are outputing debug messages - show the rest of the code there.

Apparently windows / widgets don't get a system window ID by default and are called non-native or alien.
While setAttribute(Qt::WA_NativeWindow); did not have an effect, winId did: http://qt-project.org/doc/qt-4.8/qwidget.html#winId

I'm not sure if this is a workaround or a permanent solution, so any comments are still welcome..