Weird behavior of QT windows on Linux

deisik

I have a main window (QMainWindow) which has a child widget (QDialog) and a window (another QDialog) on top of them (without a parent). When I hit the Minimize button on the first widget, the widget is minimized together with the main window (like it was modal). If I then close the second widget, the main window is restored

This happens only when the second widget is visible and only on Linux. I tested it with two window managers (IceWM and openbox) -- the behavior is the same. On Windows only the widget is minimized (as should be)

So the issue seems to be X related

deisik

In the sample code below the widgets are shown by first double-clicking on the main window and then double-clicking on the dialog itself

main.cpp

#include "main_window.h"
#include <QApplication>

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

    window.show();

    return app.exec();
}

main_window.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

#include "dialog.h"

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    WindowDialog *first;

    MainWindow(QWidget *parent = nullptr);

protected slots:
    void mouseDoubleClickEvent(QMouseEvent*);
};

#endif // MAINWINDOW_H

main_window.cpp

#include "main_window.h"

void MainWindow::mouseDoubleClickEvent(QMouseEvent *event) {
    if (first == 0) {
        first = new WindowDialog(this);

        first->setMinimumSize(300, 200);
        first->setWindowFlags(Qt::Dialog | Qt::CustomizeWindowHint | Qt::WindowTitleHint | Qt::WindowMinimizeButtonHint | Qt::WindowCloseButtonHint);
        first->setWindowTitle("First dialog");

        first->show();
    }
    else {
        if (first->isHidden() || first->isMinimized()) {
            first->setWindowState(Qt::WindowState::WindowActive);
            first->show();
            first->activateWindow();
        }
    }
}

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) {
    first = 0;

    showMaximized();
}

dialog.h

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>

class WindowDialog : public QDialog {
    Q_OBJECT
public:
    WindowDialog *final;

    explicit WindowDialog(QWidget *parent = nullptr);
signals:
protected slots:
    void mouseDoubleClickEvent(QMouseEvent*);
};

#endif // DIALOG_H

dialog.cpp

#include "dialog.h"

void WindowDialog::mouseDoubleClickEvent(QMouseEvent *event) {
    if (final == 0) {
        final = new WindowDialog(); // no parent

        final->setMaximumSize(200, 100);
        final->setWindowFlags(Qt::Dialog | Qt::WindowStaysOnTopHint | Qt::WindowTitleHint | Qt::WindowMinimizeButtonHint | Qt::WindowCloseButtonHint);
        final->setWindowTitle("Next dialog");

        final->show();
    }
    else {
        if (final->isHidden() || final->isMinimized()) {
            final->setWindowState(Qt::WindowState::WindowActive);
            final->show();
            final->activateWindow();
        }
    }
}

WindowDialog::WindowDialog(QWidget *parent) : QDialog{parent} {
    final = 0;
}

deisik

So how can I correct this behavior?

Put simply, the first widget (a child of MainWindow) shouldn't be on top of other windows (other than the main window) and the main window shouldn't get minimized along with it. It's okay if the child is minimized with the parent, but not the other way around

Pl45m4

@deisik

Can you reproduce the weird/incorrect behavior also when not messing around with WindowStates and WindowFlags?!
Maybe it's related to that

ChrisW67

@deisik said in Weird behavior of QT windows on Linux:

So the issue seems to be X related

Your somewhat unorthodox code works just fine here on Kubuntu 22.04, Qt 6.8, and

vendor string:    The X.Org Foundation
vendor release number:    12101011
X.Org version: 21.1.11

So this is either a windows manager difference or that you are not actually using X11 but Wayland.