Hi guys, how can I create a top level widgets? int main(int argc, char *argv[]) { QApplication a(argc, argv); QWidget w1; // is it top level widget? QWidget w2; // is it top level widget? w1.show(); QString ptrStr1 = QString("0x%1").arg((quintptr)w1.windowHandle(), QT_POINTER_SIZE * 2, 16, QChar('0')); QMessageBox::information(&w1, "Info1", ptrStr1, QMessageBox::StandardButton::Ok); // ok, correct window handle w2.show(); QString ptrStr2 = QString("0x%1").arg((quintptr)w2.windowHandle(), QT_POINTER_SIZE * 2, 16, QChar('0')); QMessageBox::information(&w2, "Info2", ptrStr2, QMessageBox::StandardButton::Ok); // but 0x00000000 return a.exec(); } Whats wrong? Thanks a lot.

Instantiating a QWidget and calling show() create a series of events that get processed asynchronously. It cannot be safely assumed that windowHandle() returns a valid pointer right after construction and/or calling show() . You might be more lucky on Win10, than on UBuntu/X11. If you want to wait for the widget to be fully constructed, you have to wait for windowHandle() != nullptr , e.g. by while (!w1.windowHandle()) a.processEvents(); QWindow::isExposed() tells if the window has been rendered on a screen.

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QWidget top level widget

Unsolved General and Desktop

21 Posts 5 Posters 2.4k Views 3 Watching

A Alexey Serebryakov

@mrjj is it correct code?

class Widget : public QWidget
{
    Q_OBJECT
public:
     Widget(QWidget *parent = nullptr) : QWidget(parent, Qt::Window) {}
    ~Widget();
};

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

    Widget w1;
    Widget w2;

    w1.show();
    w1.windowHandle()->setScreen(QApplication::screens()[0]);

    w2.show();
    w2.windowHandle()->setScreen(QApplication::screens()[1]);

    return a.exec();
}

zoujiu

wrote on

#21

@Alexey-Serebryakov thank you