Restoring a Window's Geometry

This document describes how to save and restore a window's geometry using the geometry properties. 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 might not work because an invisible window does not 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, some window managers fail to implement this feature.

Since version 4.2, Qt provides functions that saves and restores a window's geometry and state for you. QWidget::saveGeometry() saves the window geometry and maximized/fullscreen state, while QWidget::restoreGeometry() restores it. The restore function also checks if the restored geometry is outside the available screen geometry, and modifies it as appropriate if it is:

 void MyMainWindow::closeEvent(QCloseEvent *event)
 {
     QSettings settings("MyCompany", "MyApp");
     settings.setValue("geometry", saveGeometry());
     settings.setValue("windowState", saveState());
     QMainWindow::closeEvent(event);
 }
 void MainWindow::readSettings()
 {
     QSettings settings("MyCompany", "MyApp");
     restoreGeometry(settings.value("myWidget/geometry").toByteArray());
     restoreState(settings.value("myWidget/windowState").toByteArray());
 }

If those functions are not available or cannot be used, then 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 Application example.

Notes provided by the Qt Community

No notes