Qt 5.9 | Best Practice Guides | Restoring a Window's Geometry

Qt 5.9.9 Reference Documentation

# 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 QWindow::geometry() and calling QWindow::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.

When using Qt Widgets, Qt provides functions that saves and restores a widget 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());
      }

Another 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.