Window Geometry

Restoring a Window's Geometry

A common task in modern applications is to restore a window's geometry in a later session. On Windows, this is basically storing the result of QWidget::geometry() and calling QWidget::setGeometry() in the next session before calling show(). On X11, this won't work because an invisible window doesn't have a frame yet. The window manager will decorate the window later. When this happens, the window shifts towards the bottom/right corner of the screen depending on the size of the decoration frame. Although X provides a way to avoid this shift, our tests have shown that almost all window managers fail to implement this feature.

A workaround is to call setGeometry() after show(). This has the two disadvantages that the widget appears at a wrong place for a millisecond (results in flashing) and that currently only every second window manager gets it right. A safer solution is to store both pos() and size() and to restore the geometry using QWidget::resize() and move() before calling show(), as demonstrated in the following code snippets (from the Application example):

    void MainWindow::readSettings()
    {
        QSettings settings("Trolltech", "Application Example");
        QPoint pos = settings.value("pos", QPoint(200, 200)).toPoint();
        QSize size = settings.value("size", QSize(400, 400)).toSize();
        resize(size);
        move(pos);
    }

    void MainWindow::writeSettings()
    {
        QSettings settings("Trolltech", "Application Example");
        settings.setValue("pos", pos());
        settings.setValue("size", size());
    }

This method works on both Microsoft Windows and most existing X11 window managers.